Defensive line In American football , each team has eleven players on the field at one time . The specific role that a player takes on the field is called their position . Under the modern rules of American football , teams are allowed unlimited subsititution , that is teams may change any number of players after any play . This has resulted in the development of three " platoons " of players , the offense ( the team with the ball , who is trying to score ) , the defense ( the team trying to prevent the other team from scoring , and to take the ball from them ) , and the special teams ( who play in kicking situations ) . Within those platoons , various specific positions exist depending on what the player ' s main job is . Offense . In American football , the offense is the side which is in possession of the ball . It is their job to advance the ball towards the opponent ' s end zone to score points . Broadly speaking , the eleven players of the offense are broken into two groups : the five offensive linemen , whose primary job is to block , and the six backs and receivers whose primary job is advance the ball by means of either running with the ball or passing it . The backs and receivers are also commonly known as skill position players or as eligible ball carriers ( offensive linemen are not normally eligible to advance the ball during play ) . The organization of the offense is strictly mandated by the rules , there must always be exactly seven players on the line of scrimmage and exactly four players ( known collectively as " backs " ) behind it on every play . The only players eligible to handle the ball during a normal play are the four backs and the two players on the end of the line . The remaining five players ( known as " interior linemen " ) are considered " ineligible " , and may only block . Within these strictures , however , creative coaches have developed a wide array of offensive formations to take advantage of different player skills and game situations . The following positions are standard in nearly every game , though different teams will use different arrangements of them . Offensive line . The offensive line is primarily responsible for blocking . During normal play , offensive linemen do not handle the ball , unless the ball is fumble d by a ball carrier , or when a player who is normally an offensive lineman takes a different position on the field . The offensive line consists of : Backs and receivers . The six backs and receivers are those that line up outside or behind the offensive line . There are four main positions in this set of players : Depending on the style of offense the coaches have designed , the game situation , and the relative skill sets of the players , teams may run formations which contain any number of running backs , wide receivers , and tight ends , so long as the mandated " four backs and seven on the line " rule is followed . For many years , the standard set consisted of the quarterback , two running backs ( a tailback / halfback and a fullback ) , two wide receivers ( a flanker and a split end ) and a tight end . Modern teams show a wide variety of formations , from a " full house " formation with three running backs , two tight ends , and no wide receivers , to " spread " formations featuring four or five wide receivers , sometimes without any running backs . Defense . The defensive team or defense is the team that begins a play from scrimmage not in possession of the ball . The object of the defensive team is to prevent the other team from scoring . The defense accomplishes this by forcing the offense to turn the ball over , either by preventing them from achieving a first down and forcing a punt , or by forcing the offense to fumble or throw an interception . Unlike the offensive team , the rules do not restrict the defensive team into certain positions . A defensive player may line up anywhere on his side of the line of scrimmage and perform any legal action . Over time , however , defensive roles have become defined into three main sets of players , and several individual positions . Defensive line . Like their offensive counterparts , defensive linemen line up directly on the line of scrimmage , close to the ball . There are two positions usually considered part of the defensive line : Often , though not always , a defensive lineman will have his " hand ( s ) on the ground , " in a three - or four - point stance before the ball is snapped ; this distinguishes his pre - snap stance from a linebacker , who begins in a two - point stance ( ie . without a hand touching the ground ) . Linebackers . Linebacker s play behind the defensive line and perform various duties depending on the situation , including rushing the passer , covering receivers , and defending against the run . Defensive backs . Defensive back s , also known as the " secondary " , play either behind the linebackers or set to the outside , near the sidelines . Defensive backs are primarily used to defend against pass plays , by covering wide receivers and tight ends to prevent them from catching the ball , or to attempt to intercept the pass from the quarterback . Defensive backs also act as the last line of defense on running plays , and need to be able to make open field tackles , especially when the ball carrier has gotten past the other defenders . A normal complement of defensive backs includes two cornerbacks and two safeties , though specialty defensive backs ( nickelbacks and dimebacks ) can be brought in in place of linebackers and defensive lineman , when there is need to cover additional pass receivers . Defensive formations are often known by a numerical code indicating the number of players at each position . The two most common formations are the 3 – 4 defense and the 4 – 3 defense , where the first number refers to the number of defensive linemen , and the second number refers to the number of linebackers ( the number of defensive backs can be inferred , since there should be eleven players on the field . ) Thus , 3 – 4 defense will consist of three defensive linemen ( usually a nose tackle and two defensive ends ) , four linebackers , and four defensive backs ( two cornerbacks , a strong safety , and a free safety ) . Special teams . Special teams are units that are on the field during kicking plays . While many players who appear on offensive or defensive squads also play similar roles on special teams ( offensive linemen to block , or defensive players to tackle ) there are some specialist roles which are unique to the kicking game .