A silent count is a signal to snap the football that is used without words.
In very loud environments it can be hard for the offense to hear the quarterback call out the snap count. This can lead to players being slow or offsides. A silent count tells the center to snap the ball without his having to hear. If the quarterback is under center, this can be the quarterback pushing on the center. If the quarterback is in shotgun, he may lift his leg to tell the center to snap.
Most of the offense looks at the ball to tell when the play has started. Usually the tackles can’t see the ball as well and need to watch the defense, so they don’t always watch. When they don’t watch, they usually have the guard hold their hand. When the guard sees the ball snapped he let’s go of the tackle’s hand, letting him know the play has started.
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