Formation ( American football ) A formation in American football refers to the position players line up in before the start of a down . There are both offensive and defensive formations and there are many formations in both categories . Offense . At the highest level of play in the NFL and NCAA , the one constant in all formations is the offensive line , consisting of the left and right tackle , left and right guard , and a center . These five positions are often referred to collectively as the " line " , and have the primary role of blocking . By rule there must be two additional players on the line of scrimmage called Ends . These players are eligible receivers and may play near the linemen ( tight ends ) or farther away ( split end or wide receiver ) . Most teams play additional players near ( but still off ) the line of scrimmage to act as extra pass receivers . Offensive positions . Up to four players can be behind the line of scrimmage , but one is always designated the quarterback ( defined as the player who receives the ball from the center ) . Upon the snap of the ball , the quarterback becomes the " ball carrier " . The ball carrier has five options : The three other backs can be halfbacks , ( who primarily carry the ball ) , fullbacks , ( who primarily block ) , or they can play near ( but not on ) the line of scrimmage to act as extra tight end s or wide receivers . A tight end that fills the role as the 4th back is often called an " H - Back " and a wide receiver that fills that role is sometimes known as a " flanker " or a " slot " receiver ( depending on where he lines up ) . Most formations have a " strong " side ( the side with the tight end , or the side with more players ) and a " weak side " ( the side opposite the tight end , or the side with fewer players ) . The ends , which may be either wide receiver s , or tight end s , may catch a passed ball or receive a handoff . Descriptions and diagrams to display offensive formations typically use the following symbols : Rules . The offense is required to set up a formation before a play , subject to several rules : Defense . Two terms often heard in referring to defensive formations are " box " and " secondary " . The " box " is defined as an area on the defensive side of the ball , within 5 yards of the line of scrimmage and framed by the offensive tackles . This area is most commonly occupied by defensive linemen and linebackers . The " secondary " can refer to the defensive backs as a group , or to the area behind the linebackers usually occupied by defensive backs . The two standard NFL defenses , the 4 - 3 and the 3 - 4 , have 7 players in the box . The phrase " 8 in the box " is used to indicate that 1 of the 2 safeties has moved into the box to defend against the run . Defensive positions . The three basic defensive positions are : Rules . Rules regarding defensive formations are not as complex as their offensive counterparts . The defense may line up anywhere on its side of the neutral zone , and players are free to move at any time before the snap , but all defensive players must remain on their side of the neutral zone ( defined as the width of the ball ) before the snap . If they line up on the wrong side of the line , the offending player ( s ) are offsides . This formation assumes the offense is lined up strong side right ( from the offense ' s point of view ) . This diagram could be matched up to an offensive formation diagram to make a complete 22 player football field .