Illegal motion is a penalty in football called against offensive players who are in motion toward the line of scrimmage during the snap. This rule prevents offensive players from getting a running start by moving toward the line of scrimmage as the play starts. The penalty results in a loss of five yards for the offense.
The illegal motion rule prevents offensive players from moving towards the line of scrimmage when the ball is snapped. Teams are allowed one player in the backfield to be in motion when the ball is snapped as long as he is moving parallel to or away from the line of scrimmage. The remaining offensive players must be stationary in their positions.
Unlike motion towards the line of scrimmage, motion parallel to or away from the line of scrimmage is acceptable because it gives the quarterback a chance to observe the type of scheme the defense is using based on the way they react. Additionally, players must be allowed the chance to go in motion when the quarterback changes the play at the line of scrimmage.
Eligible receivers are allowed to move to another spot on the line of scrimmage, but they must reset to a stationary position before the ball is snapped. Failure to reset before the play starts is considered an illegal motion penalty. The same rule applies for players in the backfield. Running backs and quarterbacks are allowed to move towards the line of scrimmage prior to the ball being snapped as long as they come to a complete stop at least one full second before the play starts. Failure to do so results in an illegal motion penalty.
The illegal motion rule is in place to prevent offensive players from getting a running start before the play starts. Players with a running start would have an unfair advantage over defenders. However, most of the time when the illegal motion penalty is called, the player penalized has no intention of getting a running start before the play begins. In the majority of cases, the player at fault simply fails to come to a complete stop when shifting positions on the line of scrimmage.
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The illegal motion penalty results in a loss of five yards for the offense.
To signal an illegal motion penalty, the referee extends one arm in a horizontal position. The referee then bends their arm at the elbow and positions their hand so that it is parallel to the ground.