In American Football and Canadian Football, not all players on offence are entitled to receive a forward pass. Only an eligible pass receiver may legally catch a forward pass, or be more than five yards over the line of scrimmage on a forward passing play. If the pass is received by a non-eligible receiver, the penalty for ineligible receiver is assessed (the play is treated as an incomplete pass, unless the ball is downed behind the line of scrimmage - in either case a down is lost). If a non-eligible receiver is more than five yards downfield on a completed forward pass, the penalty assessed is "ineligible receiver downfield" (a loss of yardage, but not loss of down).

In both forms of football, every player on the defensive team is considered eligible. The offensive team must have at least seven players lined up on the line of scrimmage. Of the players on the line of scrimmage, only the two players on the ends of the line of scrimmage are eligible receivers. The four remaining players in the backfield (five in Canadian football), including the quarterback, are also eligible receivers—except in the National Football League, where a quarterback who takes the snap directly from the center is never eligible. However, a quarterback who receives a longer snap from the center, such as in a shotgun formation, is eligible even in the NFL.

With the assignment of numbers to positions, a player who is not wearing a number that corresponds to an eligible receiver is not eligible even if he lines up in an eligible position. However, in the American game, a person who reports to the referee that he will be eligible on the play is allowed to line up and act as an eligible receiver.

If, for example, eight men line up on the line of scrimmage, the team loses an eligible receiver. This can often happen when a flanker or slot receiver, who is supposed to line up behind the line of scrimmage, instead lines up on the line of scrimmage between the offensive line and a split end. In most cases where a pass is caught by an ineligible receiver, it is usually because the quarterback was under pressure and threw it to an offensive lineman out of desperation.

Before the snap of the ball, in the American game, eligible receivers may only move parallel to the line of scrimmage, only one eligible receiver may be in motion at any given time, and if forward motion has occurred, the receiver must be still for a full second before the snap. The receiver may be in motion laterally or away from the line of scrimmage at the snap. A breach of this rule results in a penalty for illegal procedure (five yards). However, in the Canadian game, eligible receivers may move in any direction before the snap, any number may be in motion at any one time, and there is no need to be motionless before the snap.

The rules on eligible receivers only apply to forward passes, even those behind the line of scrimmage. However, any player may legally catch a backwards or lateral pass.

In the American game, once the play has started, players can become ineligible and eligible depending on how the play develops. Any eligible receiver that goes out of bounds is no longer an eligible receiver and cannot receive a forward pass. Also, if a pass is touched by any eligible receiver (tipped by a defensive lineman, slips through a receiver's hands, etc) every player on the field immediately becomes eligible. These rules may also apply to the Canadian game as well, but are not verified.

See also

• Glossary of American football

American football terminology | Canadian football terminology