NFL Official Signals

Holding

When a member of either team, um, holds an opponent. Signal: Referee puts fist in air near his face, palm facing inward, and grabs his arm with his other hand, pulling it down. Linemen are allowed to push and shove, but not to grab their opponent. There's a little holding on every play, but the most blatant holds win a flag. If you see a flag in the backfield before the ball is thrown, it's probably holding on the offense.

False Start

When a member of the offense moves before the ball is snapped. Signal: Referee puts fists in air in front of chest and moves them around each other in circles. The offense is not permitted to move, so that the defense will know when the ball is snapped, because then everyone will start moving. This penalty stops play, so if you hear a whistle before the snap, and didn't see any encroachment, it's either this or a delay of game penalty.

Pass Interference

Through holding, pushing, or shoving, when a defender interferes with the receivers ability to catch the ball, or when the receiver similarly interferes with the defender. Signal: Ref pantomimes pushing someone who is right in front of him. This penalty can often be a pretty big judgment call, and given the severity of the penalty, can lead to high tempers all around. Once the receiver is in the act of catching the ball, however, the defender is free to tackle him and cause an incompletion.

Delay of Game

When the play clock runs out before the offense snaps the ball. Signal: Ref puts hands on head, elbows out. After the end of one play, the offense has snap the ball for another play within thirty seconds. Once lined up, they have to snap the ball within ten seconds. Otherwise they get called for delay of game. The TV will helpfully display the play clock on the screen once it gets down to a few seconds.

Face Mask

When a player grabs another player by the helmet's face mask. Signal: Ref pantomimes pulling on his imaginary facemask. Neck injuries are bad. You are not allowed to put your hands anywhere near your opponents face mask. It's five yards for some of such contact, fifteen if you actually grab the mask.

Personal Foul

Signal: Ref pantomimes pulling on his imaginary facemask.

Unsportsmanlike Conduct