A forward pass, legal or illegal, is incomplete and the ball becomes dead when the pass touches the ground or goes out of bounds. It is also incomplete when a player in is the air possesses the pass and alights so that his first contact with the ground or with anything other than a player or game official is on or outside a boundary. When an incompletion occurs the down counts unless the pass is after a change of possession. If the pass is legal, the passing team next snaps the ball at the previous spot, unless lost after fourth down.
Tag: snaps
Rule 8, Section 5, Article 1
Responsibility for forcing the ball from the field of play across a goal line is attributed to the player who carries, snaps, passes, fumbles or kicks the ball, unless a new force is applied to a grounded backward pass, kick or fumble.
a. The muffing or batting of a pass, kick or fumble in flight is not considered a new force; and
b. The accidental touching of a loose ball by a player who was blocked into the ball is ignored and does not constitute a new force.
The Zebra Files 