snap

[Warrenkicker]

3-4-6 The ball remains dead and a down is not begun if a snap or free-kick is attempted before the ball is ready for play, or there is an illegal snap, other snap infraction or a dead-ball foul occurs.

2-40-2 The snap begins when the snapper first moves the ball legally other than in adjustment. In a snap, the movement must be a quick and continuous backward motion of the ball during which the ball immediately leaves the hand(s) of the snapper and touches a back or the ground before it touches an A lineman.

So in the original situation the ball hit a lineman, the snapper's knee, before it touched a back or the ground so it was an illegal snap.