Teams are allowed to substitute players on the field with players from the sideline throughout the game, and this happens between just about every play. Teams can even substitute as many players as they want. However, there are limits on how and when substitutions can be made. An obvious example is that it is illegal to make a substitution during a play. Others, though, are not so obvious:
& A offense substitute must proceed to the area between the numbers painted on either side of the field;
& Any substitute on offense that approaches the huddle and talks to a teammate must stay in for at least one play; and
& If there is a substitution on offense, the offense must wait to snap the ball until the defense is able to respond with its own substitutions; no “quick” snaps are allowed to try to get the defense to commit a penalty, like having too many players on the field. The umpire prevents this by standing over the ball until the referee determines that the defense has had a “reasonable” opportunity to make personnel changes.
Note that these rules only apply to “substitutes.” The rules define a “substitute” as a player who “is withdrawn from the game and does not participate in a least one play.” Therefore, if a player comes off the field by mistake, he can return to the field without entering the area between the numbers.
So, what’s the point of these rules? Fairness. The idea is to prevent teams from attempting to confuse the opponent unfairly. It would be unfair to not let the other team get a clear view of the opposing players who are on the field, and with enough time to make any adjustments it needs based on that personnel.
If you thought there was no significance to the players’ jersey numbers, you were wrong. Players on offense must have jersey numbers in specific ranges to be eligible to play certain positions. For example, wide receivers must wear numbers 10-19 and 80-89; tight ends must wear numbers 80-89. However, a team can allow an otherwise ineligible player (e.g., an offensive lineman) to line up in a formation as an eligible receiver (or vice versa) if it follows the following rules:
& The player must immediately report the change in his status to the referee, who will inform the defense;
& That player must participate according to his changed status as long as he is continuously in the game;
& Prior to each play, he must again report his status to the referee, who repeats his announcement to the defense; and
& The player can only change back to his previous status if he leaves the field for one play, or after one of several events: a team timeout, the end of a quarter, a score or the two-minute warning, among others.
You may recall that the offense must remain completely still in the moments immediately before the snap; any movement, no matter how slight, may draw a “false start” penalty. “But wait,” you may ask, “I know I’ve seen players moving around, running back and forth, before the ball is snapped. What gives?” Excellent question. There are, naturally, a few exceptions:
& Receivers: Eligible receivers are allowed to change position or stance before the snap. However, they must “reset” prior to the ball being snapped.
& Shifts: One or more players on offense may “shift” one or more times before the snap. However, after the last shift, all players must stop and be “set” for at least one second.
& Quarterback: If the quarterback has lined up directly behind, or “under,” the center, he is allowed to go in motion, usually stepping back. However, he can’t do it using quick or abrupt movements and he must come to a stop before the snap.
& Players in motion: It is legal for one player in the backfield (that is, positioned behind the line of scrimmage) to be moving when the ball is snapped. However, that player must be moving parallel to or away from the line of scrimmage; no player may be moving toward the line of scrimmage before the ball is snapped.
If all of this seems like a lot to keep track of, it is. That’s why there are so many officials on the field: the referee, umpire, linesman and line judge are the primary arbiters of the action near the line of scrimmage, so they will be the ones to throw the flags for these infractions. The back judge also keeps an eye out for illegal substitutions. After reading this, you probably also realize that a lot more happens on the field than what you see on TV. So, cut the officials a break next time you think they missed something at or before the snap, OK?