American Football NCAA Rule 4-1-3-a, b and p
a. When it goes out of bounds other than a kick that scores a field goal after touching the uprights or crossbar; when a ball carrier is out of bounds; or when a ball carrier is so held that their forward progress is stopped. When in question, the ball is dead (A.R. 4-2-1-II).
b. When any part of the ball carrier’s body, except the hand or foot, touches the ground or when the ball carrier is tackled or otherwise falls and loses possession of the ball as they contact the ground with any part of their body, except the 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).
p. When an airborne pass receiver of either team is held so that they are prevented from immediately returning to the ground (A.R. 7-3-6-III).