1. Substitutions
Rule 3 Section 4

2. Substitution Infractions
Substitute Infractions
Substitution Infractions
A departing player must leave the huddle within three seconds after being replaced
A departing player or substitute unsuccessfully attempts to withdraw
Team A may not break the huddle with more than 11 players
Team A rushes quickly to the line to obviously create a disadvantage for the defense
A replaced player leaves the field other than their own team sideline
A substitute enters during the down and does not participate
A substitute enters from outside his team area
A substitute becomes a player, withdraws and re-enters during the same dead-ball interval. Exception there is a charged team time-out, referees timeout, or end of quarter.
12 players participate at the snap or free kick.

3. Case Studies of Illegal Substitutions
Play Situations
Case Studies of Illegal Substitutions
Quarterback is barking signals, the referee realizes that Team A has 12 players on the field, no team A player attempts to leave the field. Ruling Dead ball foul five yard penalty
Team A breaks their huddle and moves to the line. As the quarterback is barking signals, the referee counts 11 Team A players. A 42 enters the field and no Team A player departs. Ruling Team A is given an opportunity for the replaced player to depart, allow three seconds for the player to leave if no player departs, kill the play and penalize 5 yards.

4. Case Plays Illegal Substitution
Without having substituted since the previous play, Team A (1) quickly breaks the huddle or (2) without huddling, rushes to the line of scrimmage, sets for a second, and snaps the ball.
Ruling Legal play as team A did not make any substitutions
Kicking specialists A2 enters the 10 man huddle just as it is breaking A2 quickly assumes his normal kicking position. The umpire stands over the ball to prevent the snap, but B does not react. The play clock expires just as team B begins the substitution process. Ruling Team A is charged with a delay of game penalty and warned as another instance will be an unsportsmanlike like conduct foul

5. Case Plays Illegal substitution
Third and 10 on the A-30 The play results in a completed pass for a first down but the punter A25 thinks the pass was incomplete and runs onto the field. When A 25 arrives in his team’s huddle, he realizes his team has a first down, so he runs off the field.
Ruling foul for illegal substitution