The NFL has a couple of different penalties for defensive movement before the ball is snapped. Specifically there are three penalties in the same penalty family that all share the same hand signal (hands to hips) and yardage (5yd, no automatic first down): Offsides, Neutral Zone Infraction and Encroachment. Why are there so many? Why are the nuances between them so complicated that even veteran hall of fame quarterback commentators sometimes confuse them? Hopefully after reading this they will make more sense.
To understand the offsides penalties, you must understand the False Start penalty. A False Start is sudden movement by the offense that simulates the snap. It?s always a dead ball foul, i.e. a foul that happens when a play is not ongoing ? the game is stopped right away and the play that was about to start never happens. It?s a penalty because it would be unfair for the offense to be able to deceive when the snap will actually happen.
Defensive Offsides occurs when a defensive player is on the offense?s side of the ball when the ball is snapped (or in the ?neutral zone?, defined as the length of the football ? neither team can line up here). An ?airspace violation? is enough, there?s no need to step across.
This is not a dead ball foul and play is allowed to continue ? these are the ones where a smart quarterback will realize that there will be a defensive foul and it?s a ?free play? to try to land a deep ball. After all, even if it is intercepted, the play will be called back anyway. If it lands, you just decline the penalty and take the big gain.
The defense is allowed to be on the offense?s side (or in the neutral zone) before the ball is snapped, provided they get back to their own side before the snap.
Offsides, Unabated to the Quarterback
This is a variation of a regular defensive Offsides penalty (sometimes called only as ?unabated to the quarterback? or even ?unabated?). The only difference is that this is a dead ball foul for safety reasons ? the referee thought that the play was too dangerous to be allowed to start because a defensive player had a free, quick shot at the quarterback (because the offensive line was still stationary, waiting for the snap).
Neutral Zone Infraction
Neutral Zone Infraction, or NZI, occurs when an offensive player commits a False Start due to a defender coming across to the offense?s side before the snap. Because the False Start was due to a defender starting early, it is called as a penalty for the defense. It is not Offsides because it does not require the ball to be snapped, and like a False Start it is always a dead ball foul.
Encroachment occurs when a defensive player touches an offensive player before the snap. It?s not Offsides because it doesn?t require the ball to be snapped, and it?s not Neutral Zone Infraction because it doesn?t require the offensive player to move. It?s always a dead ball foul.