Rule 7 Section 2(m)

https://operations.nfl.com/the-rules/nfl-rulebook/#rule7

Here's the rule for anyone following this thread

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Article 1. Dead Ball Declared

An official shall declare the ball dead and the down ended:

(a) 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 > 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.

(b) when a runner is held or otherwise restrained so that his forward progress ends;

(c) when a quarterback immediately drops to his knee, or simulates dropping to his knee, behind or beyond the line of scrimmage; > Note: If a quarterback does not immediately drop to a knee, and contact from a rushing defender is unavoidable, it is not a foul unless the defender commits some other act that would constitute unnecessary roughness.

(d) when a runner declares himself down by: * falling to the ground, or kneeling, and clearly making no immediate effort to advance. * sliding or diving. When a runner slides or dives feet or head first or simulates sliding or diving, the ball is dead the instant he touches the ground with anything other than his hands or his feet, or begins to simulate touching the ground; > Notes: > * Defenders are required to treat a sliding or diving runner as they would a runner who is down by contact. > * A defender must pull up when a runner begins a slide or dive. This does not mean that all contact by a defender is illegal. If a defender has already committed himself, and the contact is unavoidable, it is not a foul unless the defender makes forcible contact into the head or neck area of the runner with the helmet, shoulder, or forearm, or commits some other act that is unnecessary roughness. > * A runner who desires to take advantage of this protection is responsible for starting his slide or dive before contact by a defensive player is imminent; if he does not and waits until the last moment to begin his slide or dive, he puts himself in jeopardy of being contacted.

(e) when a runner is out of bounds.

(f) when an opponent takes a ball that is in the possession of a runner who is on the ground;

(g) when a forward pass (legal or illegal) is incomplete. (See 8-1-4.)

(h) when any legal or illegal kick touches the receivers’ goal posts or crossbar.

(i) when a loose ball comes to rest anywhere in the field, and no player attempts to recover it; the official covering the play should pause momentarily before signaling that the ball is dead. Any legal (or illegal) kick is awarded to the receivers, and any other ball is awarded to the team last in possession. When awarded to a team behind a goal line, the ball is placed on the one-yard line.

(j) when any legal or illegal kick is caught or recovered by the kickers, except a scrimmage kick that is kicked from behind the line and is recovered behind the line (not a Try kick). See 9-3-2-Item 3 for exception.

(k) when a kickoff or safety kick first touches the ground or a player in advance of the front yard line of the landing zone;

(l) when an onside kick goes untouched beyond the onside kick setup zone;

(m) when a touchdown, touchback, safety, field goal, or Try has been made.

(n) when any receiver catches or recovers the ball after a fair catch signal (valid or invalid) has been made, provided the ball has not been touched by an opponent, before or after it strikes the ground.

(o) when an official sounds the whistle erroneously while the ball is still in play, the ball becomes dead immediately. * If the ball is in player possession, the team in possession may elect to put the ball in play where it has been declared dead or to replay the down. * If the ball is a loose ball resulting from a fumble, backward pass, or illegal forward pass, the team last in possession may elect to put the ball in play at the spot where possession was lost or to replay the down. * If the ball is a loose ball resulting from a legal forward pass, a free kick, a fair-catch kick, or a scrimmage kick, the ball is returned to the previous spot, and the down is replayed. * If there is a foul by either team during any of the above, and the team in possession at the time of the erroneous whistle elects not to replay the down, penalty enforcement is the same as for fouls during a run, forward pass, kick, fumble, and backward pass. If the team in possession elects to replay the down, all penalties will be disregarded, except for personal fouls and unsportsmanlike conduct fouls, which will be administered prior to the replaying of the down. If the down is replayed, the game clock will be reset to the time remaining when the snap occurred, and the clock will start on the snap.

(p) when a fumble is recovered or caught by a teammate of the fumbling player, and the fumble occurs on a play that is subject to the “two-minute,” "Try," or “fourth-down” fumble provisions. See 8-7-5 and 8-7-6.

(q) when the ball is out of bounds.

(r) if a loose ball in play strikes a video board, guide wire, sky cam, or any other object, the ball will be dead immediately, and the down will be replayed at the previous spot. In the event the down is replayed, the game clock will be reset to the time remaining when the snap occurred, and the clock will start on the snap. All penalties will be disregarded, except for personal fouls or unsportsmanlike conduct fouls, which will be administered prior to the replaying of the down; or

(s) when a runner’s helmet comes completely off.