The Tuck Rule

I don;t like the rule, and can't really think of its purpose. But I guess it is sort of like a check swing in baseball that crosses the plate - its a strike. So here, if his arm goes forward, its a pass until he brings the ball back to his body. Hence there is no sack.

I've yet to hear a good reason for the rule.

^ NFL Rule 3, Section 21, Article 2, Note 2: "When a Team A player is holding the ball to pass it forward, any intentional forward movement of his arm starts a forward pass, even if the player loses possession of the ball as he is attempting to tuck it back toward his body. Also, if the player has tucked the ball into his body and then loses possession, it is a fumble."