When a referee throws his hat in American football, it can mean two things:

• Ineligible receiver: If a player goes out of bounds and re-enters the field of play, he becomes an ineligible receiver unless he re-establishes himself by taking three steps within the field of play. When this happens, referees throw their hats to mark the spot where the player left the field of play.

• Second penalty: If a referee throws his flag to call a penalty but sees that another penalty happens, he will throw his hat to mark the place where the second penalty happens. This is because officials carry only one flag with them, and the hat is used as a backup marker.

Referees hats are also occasionally used as markers. If a player who is not carrying the ball steps out of bounds, the official will drop his hat to mark the spot where the player went out of bounds.