A snap infraction is a dead ball penalty that occurs when the center simulates a snap or moves the ball after touching other than when snapping it.
Once the center gets in his stance and holds the ball, he cannot then make any movement that is like a snap, other than the snap. He cannot pretend to snap or move in such a way to try to draw the defense off sides. If he moves before the snap, it is a false start, like any other player. If he makes some movement with the ball, other than a snap, it is a snap infraction.
The center can’t move the ball forward either, such as a slight forward movement before a regular snap. Sometimes long snappers do this, and it is a penalty.
The center can let go of the ball and get reset, but he has to do it in such a way that it in no way simulates a snap. Usually this is done by lifting the hand vertically off the ball.
Note that the rule doesn’t proscribe the ball must be snapped between the center’s legs. That is done for other reasons not because the rule requires it.
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