# List of gridiron football rules

The following is a description of the various and alternating rules of gridiron football. Numerous leagues or organizations tend to send a laundry list of rules in order to better distinguish themselves from their counterparts.

## American football (general)
### Field and players

American football is played on a football field that is 360 by 160 feet (109.7 by 48.8 m). The longer boundary lines are sidelines, while the shorter boundary lines are end lines. Sidelines and end lines are out of bounds. Near each end of the field is a goal line; they are 100 yards (91.4 m) apart. A scoring area called an end zone extends 10 yards (9.1 m) beyond each goal line to each end line. The end zone includes the goal line but not the end line. While the playing field is effectively flat, it is common for a field to be built with a slight crown—with the middle of the field higher than the sides—to allow water to drain from the field.
Yard lines cross the field every 5 yards (4.6 m), and are numbered every 10 yards from each goal line to the 50-yard line, or midfield (similar to a typical rugby league field). Two rows of short lines, known as inbounds lines or hash marks, run at 1-yard (91.4 cm) intervals perpendicular to the sidelines near the middle of the field. All plays start with the ball on or between the hash marks. Because of the arrangement of the lines, the field is occasionally referred to as a gridiron.
At the back of each end zone are two goalposts (also called uprights) connected by a crossbar 10 feet (3.05 m) from the ground. For high skill levels, the posts are 222 inches (5.64 m) apart. For lower skill levels, these are widened to 280 inches (7.11 m).
Each team has 11 players on the field at a time. However, teams may substitute for any or all of their players, if time allows, during the break between plays. As a result, players have very specialized roles, and, sometimes (although rarely) almost all of the (at least) 46 active players on an NFL team will play in any given game. Thus, teams are divided into three separate units: the offense, the defense and the special teams.

### Start of halves

Similarly to association football, the game begins with a coin toss to determine which team will kick off to begin the game and which goal each team will defend. The options are presented again to start the second half; the choices for the first half do not automatically determine the start of the second half (i.e. it is possible for the same team to kick off both halves). The referee conducts the coin toss with the captains (or sometimes coaches) of the opposing teams. The team that wins the coin toss has three options:
* They may choose whether to kick or receive the opening kickoff.
* They may choose which goal to defend.
* They may choose to defer the first choice to the other team and have first choice to start the second half.
Whatever the first team chooses, the second team has the option on the other choice (for example, if the first team elects to receive at the start of the game, the second team can decide which goal to defend).
At the start of the second half, the options to kick, receive, or choose a goal to defend are presented to the captains again. The team which did not choose first to start the first half (or which deferred its privilege to choose first) now gets first choice of options.

### Game duration

A standard football game consists of four 15-minute quarters (12-minute quarters in high-school football and often shorter at lower levels, usually one minute per grade [e.g. 9-minute quarters for freshman games]), with a 12-minute half-time intermission (30 minutes in the Super Bowl) after the second quarter in the NFL (college halftimes are 20 minutes; in high school the interval is 15 or 20 minutes; 10 minutes for lower grades). The clock stops after certain plays; therefore, a game can last considerably longer (often more than three hours in real time), and if a game is broadcast on television, TV timeouts are taken at certain intervals of the game to broadcast commercials outside of game action. If an NFL game is tied after four quarters, the teams play an additional period, timed like the fourth quarter, lasting up to 10 minutes. There is a coin toss in the NFL just like the beginning of the game. If the receiving team scores a touchdown during the possession, they win. If they kick a field goal, then the other team gets a possession. If they score a touchdown, they win. If they tie the score by kicking a field goal, then the next team that scores wins. If the team with the first possession turns the ball over without scoring any points, then the first team to score, wins. If the defense scores a touchdown through an interception or fumble recovery, or they get a safety, then they win. In a regular-season NFL game, if no one scores in the overtime, the game ends tied. In an NFL playoff game, multiple 15-minute overtime periods are played, as needed, to determine a winner. These periods are timed as if a game had started over. From the 2022 playoffs, teams will be guaranteed one possession to start first overtime. In the extremely rare case a game would go as far as a third OT—which has never happened in the NFL—there would be no "halftime intermission"; play would resume with a kickoff similar to a normal third quarter.
No overtime is played in NFL preseason up to 1973 & since 2021.
College overtime rules are more complicated and are described in Overtime (sport).

### Advancing the ball

Advancing the ball in American football resembles the six-tackle rule and the play-the-ball in rugby league. The team that takes possession of the ball (the offense) has four attempts, called downs, in which to advance the ball 10 yards (9.1 m) toward their opponent's (the defense's) end zone. When the offense succeeds in gaining at least 10 yards, it gets a first down, meaning the team has another set of four downs to gain yet another 10 yards or to score. If the offense fails to gain a first down (10 yards) after 4 downs, the other team gets possession of the ball at the point where the fourth down ended, beginning with their first down to advance the ball in the opposite direction.
Except at the beginning of halves and after scores, the ball is always put into play by a snap. Offensive players line up facing defensive players at the line of scrimmage (the position on the field where the play begins). One offensive player, the center, then passes (or "snaps") the ball backwards between his legs to a teammate behind him, usually the quarterback.
Players can then advance the ball in two ways:
* By running with the ball, also known as rushing.
* By throwing the ball to a teammate, known as a forward pass or as passing the football. The forward pass is a key factor distinguishing American and Canadian football from other football sports. The offense can throw the ball forward only once during a down and only from behind the line of scrimmage. The ball can be thrown, pitched, handed-off, or tossed sideways or backwards at any time.
A down ends, and the ball becomes dead, after any of the following:
* The player with the ball is forced to the ground (a tackle) or has his forward progress halted by members of the other team (as determined by an official).
* A forward pass flies beyond the dimensions of the field (out of bounds) or touches the ground before it is caught. This is known as an incomplete pass. The ball is returned to the most recent line of scrimmage for the next down.
* The ball or the player with the ball goes out of bounds.
* A team scores.
Officials blow a whistle to notify players that the down is over.
Before each down, each team chooses a play, or coordinated movements and actions, that the players should follow on a down. Sometimes, downs themselves are referred to as "plays."

### Change of possession

The offense maintains possession of the ball unless one of the following things occurs:
* The team fails to get a first down— i.e., in four downs they fail to move the ball past a line 10 yards ahead of where they got their last first down (it is possible to be downed behind the current line of scrimmage, losing "yardage"). The defensive team takes over the ball at the spot where the 4th-down play ends. A change of possession in this manner is commonly called a turnover on downs, but is not credited as a defensive "turnover" in official statistics. Instead, it goes against the offense's 4th down efficiency percentage.
* The offense scores a touchdown or field goal. The team that scored then kicks the ball to the other team in a special play called a kickoff.
* The offense punts the ball to the defense. A punt is a kick in which a player drops the ball and kicks it before it hits the ground. Punts are nearly always made on fourth down (though see quick kick), when the offensive team does not want to risk giving up the ball to the other team at its current spot on the field (through a failed attempt to make a first down) and feels it is too far from the other team's goal posts to attempt a field goal.
* A defensive player catches a forward pass. This is called an interception, and the player who makes the interception can run with the ball until he is tackled, forced out of bounds, or scores.
* An offensive player drops the ball (a fumble) and a defensive player picks it up. As with interceptions, a player recovering a fumble can run with the ball until tackled, forced out of bounds, or scores. Backward passes that are not caught do not cause the down to end like incomplete forward passes do; instead the ball is still live as if it had been fumbled. Lost fumbles and interceptions are together known as turnovers.
* The offensive team misses a field goal attempt. The defensive team gets the ball at the spot where the previous play began (or, in the NFL, at the spot of the kick). If the unsuccessful kick was attempted from within 20 yards (18.3 m) of the end zone, the other team gets the ball at its own 20-yard line (that is, 20 yards from the end zone). If a field goal is missed or blocked and the ball remains in the field of play, a defensive player may pick up the ball and attempt to advance it.
* While in his own end zone, an offensive ball carrier is tackled, forced out of bounds, loses the ball out of bounds, or the offense commits certain fouls. This fairly rare occurrence is called a safety.
* An offensive ball carrier fumbles the ball forward into the opposing end zone, and then the ball goes out of bounds. This extremely rare occurrence leads to a touchback, with the ball going over to the opposing team at their 20-yard line (Note that touchbacks during non-offensive special teams plays, such as punts and kickoffs, are quite common).

### Scoring

A team scores points by the following plays:
* A touchdown (TD) is worth 6 points. It is scored when a player runs the ball into or catches a pass in his opponent's end zone. A touchdown is analogous to a try in rugby. Unlike rugby, a player does not have to touch the ball to the ground to score; a touchdown is scored any time a player has possession of the ball but not while the ball is on or beyond the opponents' goal line (or the plane above it).
** After a touchdown, the scoring team attempts a try (which is also analogous to the conversion in rugby). The ball is placed at the other team's 3-yard (2.7 m) line (the 2-yard (1.8 m) line in the NFL on 2-point conversions or 15-yard (13.7 m) for 1-point conversions). The team can attempt to kick it over the crossbar and through the goal posts in the manner of a field goal for 1 point (an extra point or point-after touchdown (PAT)), or run or pass it into the end zone in the manner of a touchdown for 2 points (a two-point conversion). In college football, the NFL, USFL and Texas high school football, if the defense intercepts or recovers a fumble during a one or two-point conversion attempt and returns it to the opposing end zone, the defensive team is awarded the two points.
* A field goal (FG) is worth 3 points, and it is scored by kicking the ball over the crossbar and through the goal posts (uprights). Field goals may be placekicked (kicked when the ball is held vertically against the ground by a teammate) or drop-kicked (extremely uncommon in the modern game, with only two successes in sixty-plus years in the NFL). A field goal is usually attempted on fourth down instead of a punt when the ball is close to the opponent's goal line, or, when there is little or no time left to otherwise score. A fair catch kick is also 3.
* A safety, worth 2 points, is scored by the opposing team when the team in possession at the end of a down is responsible for the ball becoming dead behind its own goal line. For instance, a safety is scored by the defense if an offensive player is tackled, goes out of bounds, or fumbles the ball out of bounds in his own end zone. Safeties are relatively rare. Note that, though even more rare, the team initially on offense during a down can score a safety if a player of the original defense gains possession of the ball in front of his own goal line and then carries the ball or fumbles it into his own end zone where it becomes dead. However, if the ball becomes dead behind the goal line of the team in possession and its opponent is responsible for the ball being there (for instance, if the defense intercepts a forward pass in its own end zone and the ball becomes dead before the ball is advanced out of the end zone) it is a touchback: no points are scored and the team last in possession keeps possession with a first down at its own 20-yard line. In amateur and pro football, in the extremely rare instance that a safety is scored on a try, it is worth only 1 point.

### Kickoffs and free kicks

Each half begins with a kickoff. Teams also kick off after scoring touchdowns and field goals. The ball is kicked using a kicking tee from the team's own 35-yard (32 m) line in the NFL and college football (as of the 2011 season). The other team's kick returner tries to catch the ball and advance it as far as possible. Where he is stopped is the point where the offense will begin its drive, or series of offensive plays. If the kick returner catches the ball in his own end zone, he can either run with the ball, or elect for a touchback by kneeling in the end zone, in which case the receiving team then starts its offensive drive from its own 20-yard line (25-yard line in NFL, since 2015). A touchback also occurs when the kick goes out-of-bounds in the end zone, or since 2018, the ball hits the ground on the goal line and in the end zone. A kickoff that goes out-of-bounds anywhere other than the end zone before being touched by the receiving team is a foul, and the ball will be placed where it went out of bounds or 30 yards (27 m) from the kickoff spot, depending on which is more advantageous to the opposite team. Unlike with punts, once a kickoff goes 10 yards and the ball has hit the ground, it can be recovered by the kicking team. A team, especially one who is losing, can try to take advantage of this by attempting an onside kick. Punts and turnovers in the end zone can also end in a touchback.
After safeties, the team that gave up the points must free kick the ball to the other team from its own 20-yard line.

### Penalties

Fouls (a type of rule violation) are punished with penalties against the offending team. Most penalties result in moving the football towards the offending team's end zone. If the penalty would move the ball more than half the distance towards the offender's end zone, the penalty becomes half the distance to the goal instead of its normal value.
Most penalties result in replaying the down. Some defensive penalties give the offense an automatic first down. Conversely, some offensive penalties result in loss of a down (loss of the right to repeat the down). If a penalty gives the offensive team enough yardage to gain a first down, they get a first down, as usual.
If a foul occurs during a down, an official throws a yellow penalty flag near the spot of the foul. When the down ends, the team that did not commit the foul has the option of accepting the penalty, or declining the penalty and accepting the result of the down.

### Variations

Variations on these basic rules exist, particularly touch and flag football, which are designed as non-contact or limited-contact alternatives to the relative violence of regular American football. In touch and flag football, tackling is not permitted. Offensive players are "tackled" when a defender tags them or removes a flag from their body, respectively. Both of these varieties are played mainly in informal settings such as intramural or youth games. Another variation is "wrap", where a player is "tackled" when another player wraps his arms around the ball carrier. Professional, intercollegiate, and varsity-level high school football invariably use the standard tackling rules.
Another variation is with the number of players on the field. In sparsely populated areas, it is not uncommon to find high school football teams playing nine-man football, eight-man football or six-man football. Players often play on offense as well as defense. The Arena Football League was a league that played eight-man football, but also had played indoors and on a much smaller playing surface with rule changes to encourage a much more offensive game.
Another variation often played by American children is called Catch and Run. In this game, the children split into two teams and line up at opposite sides of the playing field. One side throws the ball to the other side. If the opposing team catches the ball, that player tries to run to the throwing teams touchdown without being tagged/tackled. If no one catches the ball or if the player is tagged/tackled, then that team has to throw the ball to the opposing team. This repeats until the game (or recess period) is deemed over.

## Canadian football (general)
### The field

The Canadian football field is 110 yards (100 m) long and 65 yards (59 m) wide with end zones 20 yards (18 m) deep. At each goal line is a set of 40-foot-high (12 m) goalposts, which consist of two uprights joined by a 18.5-foot-long (5.6 m) crossbar which is 10 feet (3.0 m) above the goal line. The goalposts may be H-shaped (both posts fixed in the ground) although in the higher-calibre competitions the tuning-fork design (supported by a single curved post behind the goal line, so that each post starts 10 feet (3.0 m) above the ground) is preferred. The sides of the field are marked by white sidelines, the goal line is marked in white, and white lines are drawn laterally across the field every 5 yards (4.6 m) from the goal line.

### Play of the game

Teams advance across the field through the execution of quick, distinct plays, which involve the possession of a brown, prolate spheroid ball with ends tapered to a point. The ball has two one-inch-wide white stripes.

#### Kickoff

Play begins with one team place-kicking the ball from its own 35-yard (32 m) line. Both teams then attempt to catch the ball. The player who recovers the ball may run while holding the ball, or throw the ball to a teammate, so long as the throw is not forward.

#### Stoppage of play

Play stops when the ball carrier's knee, elbow, or any other body part aside from the feet and hands, is forced to the ground (a tackle); when a touchdown (see below) or a field goal is scored; when the ball leaves the playing area by any means (being carried, thrown, or fumbled out of bounds); or when the ball carrier is in a standing position but can no longer move. If no score has been made, the next play starts from scrimmage.

#### Scrimmage

Before scrimmage, an official places the ball at the spot it became dead, but no nearer than 24 yards (22 m) from the sideline or 1-yard (0.91 m) from the goal line. The line parallel to the goal line passing through the ball (line from sideline to sideline for the length of the ball) is referred to as the line of scrimmage. This line is a sort of "no-man's land"; players must stay on their respective sides of this line until the play has begun again. For a scrimmage to be valid the team in possession of the football must have seven players, excluding the quarterback, within one yard of the line of scrimmage. The defending team must stay a yard or more back from the line of scrimmage.

#### Live play

On the field at the beginning of a play are two teams of 12 (unlike 11 in American football). The team in possession of the ball is the offence and the team defending is referred to as the defence. Play begins with a backwards pass through the legs (the snap) by a member of the offensive team, to the quarterback or punter. If the quarterback or punter receives the ball, he may then do any of the following:
* run with the ball, attempting to run farther downfield (gaining yardage). The ball-carrier may run in any direction he sees fit (including backwards).
* drop-kick the ball, dropping it onto the ground and kicking it on the bounce. (This play is exceedingly rare in both Canadian and American football, although in the Canadian game it is sometimes used as a last-second "desperation play" if the team is behind by less than three points.)
* pass the ball laterally or backwards to a teammate. This play is known as a lateral, and may come at any time on the play. A pass which has any amount of forward momentum is a forward pass (see below); forward passes are subject to many restrictions which do not apply to laterals.
* hand-off—hand the ball off to a teammate, typically a halfback or the fullback.
* punt the ball; dropping it in the air and kicking it before it touches the ground. When the ball is punted, only opposing players (the receiving team), the kicker, and anyone behind the kicker when he punted the ball are able to touch the ball, or even go within five yards of the ball until it is touched by an eligible player (the No Yards rule, which is applied to all kicking plays).
* place the ball on the ground for a place kick
* throw a forward pass, where the ball is thrown to a receiver located farther downfield (closer to the opponent's goal) than the thrower is. Forward passes are subject to the following restrictions:
** They must be made from behind the line of scrimmage
** Only one forward pass may be made on a play
** The pass must be made in the direction of an eligible receiver.
Each play constitutes a down. The offence must advance the ball at least ten yards towards the opponents' goal line within three downs or forfeit the ball to their opponents. Once ten yards have been gained the offence gains a new set of three downs (rather than the four downs given in American football). Downs do not accumulate. If the offensive team completes 10 yards (9.1 m) on their first play, they lose the other two downs and are granted another set of three. If a team fails to gain ten yards in two downs they usually punt the ball on third down or try to kick a field goal (see below), depending on their position on the field.

#### Change in possession

The ball changes possession in the following instances:
* If the offence scores a field goal, the scoring team must kickoff from their own 35-yard (32 m) line.
* If the offence scores a touchdown, the scoring team must kickoff from their own 35-yard (32 m) line. This also applies when the defence scores on a turnover which is returned for a touchdown — technically, they become the offence until the conclusion of the play, and the scoring team must still kickoff.
* If the defence scores on a safety, they have the right to claim possession.
* If one team kicks the ball; the other team has the right to recover the ball and attempt a return. If a kicked ball goes out of bounds, or the kicking team scores a single or field goal as a result of the kick, the other team likewise gets possession.
* If the offence fails to make ten yards in three plays, the defense takes over on downs.
* If the offence attempts a forward pass and it is intercepted by the defense; the defense takes possession immediately (and may try and advance the ball on the play). Note that incomplete forward passes (those which go out of bounds, or which touch the ground without being first cleanly caught by a player) result in the end of the play, and are not returnable by either team.
* If the offence fumbles (a ball carrier drops the football, or has it dislodged by an opponent, or if the intended player fails to catch a lateral pass or a snap from centre, or a kick attempt is blocked by an opponent), the ball may be recovered (and advanced) by either team. If a fumbled ball goes out of bounds, the team whose player last touched it is awarded possession at the spot where it went out of bounds. A fumble by the offence in their own end zone, which goes out of bounds, results in a safety.
* If the offence has committed two consecutive time counts — failed to put the ball in play within 20 seconds of the referee declaring the ball ready for play — on third down in the last three minutes of either half, the referee has the right to give possession to the defence. (This rule does not apply on convert attempts, which are untimed downs.)
* When the first half ends, the team which kicked to start the first half may receive a kickoff to start the second half.

#### Rules of contact

There are many rules to contact in this type of football. First, the only player on the field who may be legally tackled is the player currently in possession of the football (the ball carrier). Second, a receiver, that is to say, an offensive player sent down the field to receive a pass, may not be interfered with (have his motion impeded, be blocked, etc.) unless he is within one yard of the line of scrimmage (as opposed to 5 yards (4.6 m) in American football). Any player may block another player's passage, so long as he does not hold or trip the player he intends to block. The kicker may not be contacted after the kick but before his kicking leg returns to the ground (this rule is not enforced upon a player who has blocked a kick), and the quarterback, having already thrown the ball, may not be hit or tackled.

#### Infractions and penalties

Infractions of the rules are punished with penalties, typically a loss of yardage of 5, 10 or 15 yards (14 m) against the penalized team. Minor violations such as offside (a player from either side encroaching into scrimmage zone before the play starts) are penalized five yards, more serious penalties (such as holding) are penalized 10 yards (9.1 m), and severe violations (such as face-masking) of the rules are typically penalized 15 yards (14 m). Depending on the penalty, the penalty yardage may be assessed from the original line of scrimmage, the spot the violation occurred, or the place the ball ended after the play. Penalties on the offence may, or may not, result in a loss of down; penalties on the defence may result in a first down being automatically awarded to the offence. For particularly severe conduct, the game official(s) may eject players (ejected players may be substituted for), or in exceptional cases, declare the game over and award victory to one side or the other. Penalties do not affect the yard line which the offence must reach in order to reach first down (unless the penalty results in a first down being awarded); if a penalty against the defence results in the first down yardage being attained, then the offence is awarded a first down.
Penalties may occur before a play starts (such as offsides), during the play (such as holding), or in a dead-ball situation (such as unsportsmanlike conduct).
Penalties never result in a score for the offence (a penalty by the defence committed in their end zone is not ruled a touchdown); on rare occasions, penalties against the offence in their own end zone may result in a safety being scored by the defence. If the penalty yardage, once assessed would move the ball into an end zone (or further than half the distance between the end zone and the spot the penalty is assessed from), a penalty of half-the-distance is assessed instead. Note that in Canadian football (unlike American football), no scrimmage may start inside either one-yard line.
In most cases, the non-penalized team will have the option of declining the penalty; in which case the results of the previous play stand as if the penalty had not been called. One notable exception to this rule is if the kicking team on a 3rd down punt play is penalized before the kick occurs; the receiving team may not decline the penalty and take over on downs. (After the kick is made, change of possession occurs and subsequent penalties are assessed against either the spot where the ball is caught, or the runback).

#### Kicking

Canadian football distinguishes three ways of kicking the ball:

##### Place kick

    Kicking a ball held on the ground by a teammate, or, on a kickoff (resuming play following a score), placed on a tee.

##### Drop kick

    Kicking a ball after bouncing it on the ground. Although rarely used today, it has the same status in scoring as a place kick. This play is part of the game's rugby heritage, and was largely made obsolete when the ball with pointed ends was adapted. Unlike the American game, Canadian rules allow a drop kick to be attempted at any time by any player, but the move is very rare.

##### Punt

    Kicking the ball after it has been released from the kicker's hand and before it hits the ground. Punts may not score a field goal, even if one should travel through the uprights. As with drop kicks, players may punt at any time.
On punts and field goal attempts (but not kickoffs), members of the kicking team, other than the kicker and any teammates who are onside (behind the kicker at the time of the kick), may not approach within five yards of the ball until it has been touched by the receiving team.

#### Scoring

The methods of scoring are:

##### Touchdown

    Achieved when the ball is in possession of a player in the opponent's goal area, or when the ball in the possession of a player crosses or touches the plane of the opponent's goal-line, worth 6 points (5 points until 1956). A touchdown in Canadian football is often referred to as a "major score" or simply a "major."

##### Conversion (or Convert)

    After a touchdown, the team that scored attempts one scrimmage play from any point between the hash marks on or outside the opponents' 5-yard (4.6 m) line. If they make what would normally be a field goal, they score one point; what would normally be a touchdown scores two points (a "two-point conversion"). No matter what happens on the convert attempt, play then continues with a kickoff (see below).

##### Field goal

    Scored by a drop kick or place kick (except on a kickoff) when the ball, after being kicked and without again touching the ground, goes over the cross bar and between the goal posts (or between lines extended from the top of the goal posts) of the opponent's goal, worth three points.

##### Safety

    Scored when the ball becomes dead in the possession of a team in its own goal area, or when the ball touches or crosses the dead-line, or side-line-in-goal and touches the ground, a player, or some object beyond these lines as a result of the team scored against making a play. It is worth two points. This is different from a single (see below) in that the team scored against begins with possession of the ball. The most common safety is on a third down punt from the end zone, in which the kicker decides not to punt and keeps the ball in his team's own goal area. The ball is then turned over to the receiving team (who gained the two points), and they begin their first down possession play from their own 35-yard (32 m) line on their side of the field.

##### Single

    Scored when the ball becomes dead in the possession of a team in its own goal area, or when the ball touches or crosses the dead-line, or side-line-in-goal, and touches the ground, a player, or some object beyond these lines as a result of the ball having been kicked from the field of play into the goal area by the scoring team. It is worth one point. This is different from a safety (see above) in that team scored against receives possession of the ball after the score.
    Officially, the single is called a rouge (French for "red") but is often referred to as a single. The exact derivation of the term is unknown but it has been thought that in early Canadian football, the scoring of a single was signaled with a red flag.

#### Resumption of play

Resumption of play following a score is conducted under procedures which vary with the type of score.
* Following a touchdown and convert attempt (successful or not), play resumes with the scoring team kicking off from its own 35-yard (32 m) line (45-yard line in amateur leagues).
* Following a field goal, the non-scoring team may choose for play to resume either with a kickoff as above, or by scrimmaging the ball from its own 35-yard (32 m) line.
* Following a safety, the scoring team may choose for play to resume in either of the above ways, or it may choose to kick off from its own 35-yard (32 m) line.
* Following a single or rouge, play resumes with the non-scoring team scrimmaging from its own 35-yard (32 m) line, unless the single is awarded on a missed field goal, in which case the non-scoring team scrimmages from either the 35-yard (32 m) line or the yard line from which the field goal was attempted, whichever is greater.

#### Game timing

The game consists of two 30-minute halves, each of which is divided into two 15-minute quarters. The clock counts down from 15:00 in each quarter. Timing rules change when there are three minutes remaining in a half. A 2-minute interval occurs after the end of each quarter (15 minutes at halftime, except 30 minutes in Grey Cup), and the two teams then change goals.
In the first 27 minutes of a half, the clock stops when:
* points are scored,
* the ball goes out of bounds,
* a forward pass is incomplete,
* the ball is dead and a penalty flag has been thrown,
* the ball is dead and teams are making substitutions (e.g., possession has changed, punting situation, short yardage situation),
* the ball is dead and a player is injured, or
* the ball is dead and a captain calls a time-out.
The clock starts again when the referee determines the ball is ready for scrimmage, except for team time-outs (where the clock starts at the snap), after a time count foul (at the snap) and kickoffs (where the clock starts not at the kick but when the ball is first touched after the kick).
In the last three minutes of a half, the clock stops whenever the ball becomes dead. On kickoffs, the clock starts when the ball is first touched after the kick. On scrimmages, when it starts depends on what ended the previous play. The clock starts when the ball is ready for scrimmage except that it starts on the snap when on the previous play
* the ball was kicked off,
* the ball was punted,
* the ball changed possession,
* the ball went out of bounds,
* there were points scored,
* there was an incomplete forward pass,
* there was a penalty applied (not declined), or
* there was a team time-out.
The clock does not run during convert attempts in the last three minutes of a half. If the 15 minutes of a quarter expire while the ball is live, the quarter is extended until the ball becomes dead. If a quarter's time expires while the ball is dead, the quarter is extended for one more scrimmage. A quarter cannot end while a penalty is pending: after the penalty yardage is applied, the quarter is extended one scrimmage. Note that the non-penalized team has the option to decline any penalty it considers disadvantageous, so a losing team cannot indefinitely prolong a game by repeatedly committing penalties.
In the event of a tie after regulation, teams get one possession from the opponents' 35-yard line. The overtime is untimed. Coin toss determines whether team receives first or defend; the teams turn about for the next overtime possession, if needed. Whoever is ahead after one possession wins it and two points in standings; if after two possessions in the regular season or preseason, a tie still persists, the game ends drawn, and one point in standings; however, in postseason, multiple overtime possessions are repeated until whoever is up, which wins the game. If a touchdown has been scored they must make a two-point conversion, unless they score enough beat their opponents.

## College football

Teams get 3 timeouts per half, which can't carry over to next half or overtime, plus one per overtime period (same as in the NFL, but allows two per overtime period). Although rules for the high school, college, and NFL games are generally consistent, there are several minor differences. The NCAA Football Rules Committee determines the playing rules for Division I (both Bowl and Championship Subdivisions), II, and III games (the National Association of Intercollegiate Athletics (NAIA) is a separate organization, but uses the NCAA rules).
* A pass is ruled complete if one of the receiver's feet is inbounds at the time of the catch. In the NFL both feet must be inbounds.
* A player is considered down when any part of his body other than the feet or hands touches the ground (from a tackle or otherwise), with the sole exception of the holder for field goal and extra point attempts. In the NFL a player is active until he is tackled or forced down another way by a member of the opposing team (down by contact).
* The clock stops after the offense completes a first down and begins again—assuming it is following a play in which the clock would not normally stop—once the referee declares the ball ready for play, in Division III & NAIA; the top two divisions come 2023 will see the clock run outside of two minutes left in each half. In the NFL the clock does not explicitly stop for a first down.
* Overtime was introduced in 1996, eliminating ties. Since 2021, during overtime, each team is given one possession from its opponent's twenty-five yard line with no game clock, despite the one timeout per period and use of play clock; the procedure repeats for one more possession if needed; all possessions thereafter will be from the opponent's 3-yard line. Whoever leads after both possessions will be declared the winner. If the teams remain tied, overtime periods continue, with a coin flip determining the first possession. Possessions alternate with each overtime, until one team leads the other at the end of the overtime. A two-point conversion is required if a touchdown is scored in double overtime. From triple overtime, two-point conversions are employed hereafter. (In the NFL, overtime is decided by a 10-minute sudden-death quarter, and regular season games can still end in a tie if neither team scores. Overtime for regular season games in the NFL began with the 1974 season, but reduced since 2017. In the post-season, if the teams are still tied, teams will play multiple 15-minute overtime periods until whoever scores. The first overtime, since 2022 playoffs, guarantees teams one possession.)
* Extra point tries are attempted from the three-yard line. The NFL uses the 2-yard line for 2-point conversions or 15-yard line for 1-point conversions.
* The defensive team may score two points on a point-after touchdown attempt by returning a blocked kick, fumble, or interception into the opposition's end zone. In addition, if the defensive team gains possession, but then moves backwards into the endzone and is stopped, a one-point safety will be awarded to the offense, although, unlike a real safety, the offense kicks off, opposed to the team charged with the safety. In the NFL, a conversion attempt ends when the defending team gains possession of the football.
* The two-minute warning will be used in college football and high school football in Texas come 2024, except in rare cases where the scoreboard clock has malfunctioned and is not being used.
* There is an option to use instant replay review of officiating decisions. Division I FBS (formerly Division I-A) schools use replay in virtually all games; replay is rarely used in lower division games. Every play is subject to booth review with coaches only having one challenge. In the NFL, challenges are only automatic in the final two minutes of each half or the entire overtime.
* In the 2006 season, the game clock was started when the ball was declared ready for play after the defensive team (during a scrimmage down) or the receiving kick (during a free kick down) was awarded a first down, reducing the time of games. This rule only lasted one year.
* In the 1984 season, the ball was placed on the 30-yard line (instead of the 20) if a kickoff sailed through the end zone on the fly and untouched. This rule was rescinded after one year.
* Among other rule changes to 2007, kickoffs have been moved from the 35-yard line back five yards to the 30-yard line to match that of the NFL. Some coaches and officials are questioning this rule change as it could lead to more injuries to the players as there will likely be more kickoff returns. The rationale for the rule change was to help reduce dead time in the game. However, the NFL would move its kickoffs back to the 35-yard line for the 2011 season; the NCAA followed suit one year later.
* Since the 2012 college football season, all touchbacks on kickoffs, or free kicks after a safety, have been spotted on the 25-yard line instead of the previous 20-yard spot (which remains the spot for touchbacks in all other game situations). The NFL made this same change effective with its 2018 season. In that same 2018 season, college football (and the NFL come 2023) made a further change to its touchback rule; any fair catch on a kickoff (or free kick following a safety) between the receiving team's goal line and 25-yard line is treated as a touchback, with the receiving team taking possession on its own 25.