The ruling on the field is first down.
An official shall declare the ball dead and the down ended when a runner is contacted by an opponent and touches the ground with any part of his body other than his hands or feet. The ball is dead the instant the runner touches the ground. A runner touching the ground with his hands or feet while in the grasp of an opponent may continue to advance; or 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 a touchdown.
In the field of play, if a catch has been completed, and there is contact by a defender causing the ball to come loose before the player who caught the loose ball is down by contact, it is a fumble, and the ball remains alive. It is also a fumble if the action occurs in the end zone being defended by the team of the player who caught the loose ball. If the action occurs in the opponent's end zone, it is a touchdown or a touchback.
The ruling on the field is a fumble.
A player who makes a catch may advance the ball. A forward pass is complete (by the offense) or intercepted (by the defense) if a player, who is inbounds:
a. secures control of the ball in his hands or arms prior to the ball touching the ground; and
b. touches the ground inbounds with both feet or with any part of his body other than his hands; and
c. maintains control of the ball after (a) and (b) have been fulfilled, until he has the ball long enough to clearly become a runner. A player has the ball long enough to become a runner when, after his second foot is on the ground, he is capable of avoiding or warding off impending contact of an opponent, tucking the ball away, turning up field, or taking additional steps (see 3-2-7-Item 2).
Note: If a player has control of the ball, a slight movement of the ball will not be considered a loss of possession. He must lose control of the ball in order to rule that there has been a loss of possession.
If the player loses the ball while simultaneously touching both feet or any part of his body to the ground, it is not a catch.