Formation (American football)

Most teams play additional players near (but still off) the line of scrimmage to act as extra pass receivers.

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.

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 length of the ball) before the snap.

The defense is only allowed a maximum of 6 players on the line of scrimmage on either side of the snapper at the snap.

The standard defensive formations in use at most levels of American football are the result of decades of experimentation, trial and error, along with rule changes in the 1950s that eliminated the one-platoon system and gave greater prominence to lighter, faster linebackers (prior to the 1950s, most defensive formations were mirror images of those used on offense).