An NFL referee extends both arms to stop the game or signal a score, pass interference or timeout. One arm is extended to resume play, signal illegal defensive contact on a receiver or to show a player disqualification.
Arms raised above the head follow a touchdown or successful field goal or conversion. Pass interference is shown when the arms are extended from the chest. Waving the arms above the head is used for time stoppages such as a timeout or when a play ends outside the field.
Waving the arms at waist level signals an incomplete pass or conversion attempt. A delay of game penalty is shown by the referee's crossed arms at chest level.
Grabbing of the wrist signals holding when the fist is clenched. An illegal-use-of-hands penalty is shown when the hand from the wrist is open.
A referee touches his cap with the right hand when there is an ineligible receiver during a play. Tripping is shown by moving the right foot behind the left heel. A grasping motion in front of the face is used for face-mask penalties.
For players, a kick receiver waves one hand above his head to signal a fair-catch attempt. A player or coach forms a "T" with the hands to request a timeout. Players and coaches also use hand signals as play-calling codes.