Rule 4 – Section 1 – Article 3 – Ball Declared Dead

A live ball becomes dead and an official shall sound his whistle or declare it dead:

b. When any part of the ball carrier’s body, except his hand or foot, touches the ground or when the ball carrier is tackled or otherwise falls and loses possession of the ball as he contacts the ground with any part of his body, except his hand or foot. (Exception: The ball remains alive when an offensive player has simulated a kick or at the snap is in position to kick the ball held for a place kick by a teammate. The ball may be kicked, passed or advanced by rule.) (A.R. 4-1-3:I)