The ruling on the field is a fumble.
An official shall declare the ball dead and the down ended:
Note: If, after contact by an opponent, any part of a runner’s leg above the ankle or any part of his arm above the wrist touches the ground, the runner is down.
The ruling on the field is completed pass.
A player is in possession when he is inbounds and has control of the ball with his hands or arms.
To gain possession of a loose ball that has been caught, intercepted, or recovered, a player (a) must have complete control of the ball with his hands or arms and (b) have both feet or any other part of his body, other than his hands, completely on the ground inbounds, and, after (a) and (b) have been fulfilled, perform any act common to the game (e.g., tuck the ball away, extend it forward, take an additional step, turn upfield, or avoid or ward off an opponent). It is not necessary that he commit such an act, provided that he maintains control of the ball long enough to do so. This rule applies in the field of play, at the sideline, and in the end zone.
If a player who has completed the first two, but not the third requirement for possession, contacts the ground and loses control of the ball, there is no possession if the ball hits the ground before he regains control, or if he regains control out of bounds. If a player would have caught, intercepted, or recovered a ball inbounds, but is carried out of bounds, player possession will be granted (8-1-3-Note 5).
The ruling on the field is an interception.
Item 2. Runner Out of Bounds. If the ball is in player possession when that player goes out of bounds, the out-of-bounds spot is the forward point of the ball when the ball crosses the side line, or, if the ball does not cross the sideline, the forward point of the ball at the instant the player is out of bounds.
Item 3. Runner Inbounds. If the ball, while in possession of a player who is inbounds, is declared out of bounds because of touching anything that is out of bounds, the out-of-bounds spot is the yard line through the forward point of the ball at the instant of such touching.