Teams move too soon at the start

False Start: Offense moves too early

Offside: Offensive or defensive player lined up in the zone when ball snaps or crosses the line 

Encroachment: Defender touches someone before the snap

NZI: Defender crosses line, makes an O-lineman jump  (Neutral zone infraction)

Rules about movement for the offense and defense

Defense Movement Rules

Free movement: Defenders can shift, run, or adjust their positions anywhere on their side of the line of scrimmage before the snap.
Restrictions: They cannot cross the neutral zone (offside/encroachment) or use abrupt, jerky fake signals meant to trick the offense into a false start. [1, 2, 3]

Offense Movement Rules

The stationary rule: All offensive players must come to a complete, dead stop for at least one full second in a set formation before the ball is snapped. [1]
Pre-snap motion exception: Exactly one offensive player (usually a wide receiver or running back) is allowed to be moving at the snap, provided they move laterally or backward, and not forward toward the line of scrimmage. [1, 2]
Linemen: Offensive linemen (tackles, guards, center) cannot move or shift at all once they take their stance.




While the majority of the offense must be completely still, football rules allow for specific exceptions, most notably a player in motion.
Here is exactly how the rules break down for the offense before the ball is snapped:
1. The Pre-Snap Set
Before anyone can go into motion, all 11 offensive players must come to a complete stop simultaneously. They must remain completely stationary for at least one full second.
2. Player in Motion
After that one-second pause, one offensive player who is lined up in the backfield (not on the line of scrimmage) is allowed to go into motion.
The Rule: This player can move parallel to or away from the line of scrimmage.
The Restriction: They absolutely cannot move forward toward the line of scrimmage at the time of the snap. If they are moving forward when the ball is snapped, it is a penalty for illegal motion or a false start.