Changes

The yard line on the field where the ball is located is known as the ''line of scrimmage''. The offensive players must line up on the line of scrimmage facing the opponents end zone, while the defense must be behind the line of scrimmage with their backs to their own end zone.

The yard line on the field where the ball is located is known as the ''line of scrimmage''. The offensive players must line up on the line of scrimmage facing the opponents end zone, while the defense must be behind the line of scrimmage with their backs to their own end zone.

Every play begins with the teams facing each other on the line of scrimmage, and the players may move once the ball is ''snapped'' (removed from the ground) by the [[center (football)|center]]. The center usually snaps the ball between his legs to the [[quarterback]], who may take one of several courses of action;

Every play begins with the teams facing each other on the line of scrimmage, and the players may move once the ball is ''snapped'' (removed from the ground) by the [[center (football)|center]]. The center usually snaps the ball between his legs to the [[quarterback]] (QB), who may take one of several courses of action;

[[Image:AmericanFootballPositions.png|thumb|right|300px|Typical offensive/defensive positions at the start of a play. The offensive positions are represented by blue circles, and the defensive positions are in red.]]

[[Image:AmericanFootballPositions.png|thumb|right|300px|Typical offensive/defensive positions at the start of a play. The offensive positions are represented by blue circles, and the defensive positions are in red (note: click on the picture for a guide to position abbreviations).]]

*The quarterback may hand the ball off to a rusher (usually a [[fullback]], [[halfback]], or [[runningback]]), who will attempt to run the ball down the field as far as they can before being stopped by the defense.

*The quarterback may hand the ball off to a rusher (usually a [[fullback]], [[halfback]], or [[runningback]]), who will attempt to run the ball down the field as far as they can before being stopped by the defense.

*The quarterback may opt to throw the ball to a receiver (usually a [[wide receiver]] or [[tight end]]) who is already several yards down the field. Once the receiver catches the ball, he may continue to run until brought down by a defensive player. If the receiver does not catch the ball, it is called an ''incomplete pass''.

*The quarterback may opt to throw the ball to a receiver (usually a [[wide receiver]] or [[tight end]]) who is already several yards down the field. Once the receiver catches the ball, he may continue to run until brought down by a defensive player. If the receiver does not catch the ball, it is called an ''incomplete pass''.

*The quarterback may spike the ball at the ground to stop the game clock, at the expense of a loss of a down.

*The quarterback may spike the ball at the ground to stop the game clock, at the expense of a loss of a down.

*The quarterback may run the ball down the field himself; this option is usually unwise, as an injury to the quarterback can be destructive to an entire team for the whole season.  

*The quarterback may run the ball down the field himself; this option is usually unwise, as an injury to the QB can be destructive to an entire team for the whole season.  

The play ends when the referee's whistle is blown. The whistle can be blown for several reasons;

The play ends when the referee's whistle is blown. The whistle can be blown for several reasons;