Crusader

Lets not guess about it:

ARTICLE 6. CRACKBACK BLOCK

All Crackback Blocks are illegal. It is a Crackback Block if the following conditions are fulfilled:

The block occurs within an area five yards on either side of the line of scrimmage, including within close-line play, by an offensive player who is moving toward the position from which the ball was snapped; and

(a) the offensive player was in a set position and aligned more than two yards outside an offensive tackle (flexed) when the ball was snapped; or
(b) the offensive player was in a backfield position when the ball was snapped and moved to a position more than two yards outside an offensive tackle; or
(c) the offensive player was in a backfield position and in motion when the ball was snapped.

Note: If there is a broken play, significantly changing the original direction, the crackback block is legal. When the change in direction is the result of a designed play (reverse), the restriction remains in effect.

The following is prohibited against a player who is the recipient of a Crackback Block:

(a) Contacting him below the waist;
(b) forcibly hitting his head or neck area with the helmet, facemask, forearm, or shoulder, even if the initial contact is lower than the player’s neck;
(c) lowering the head and making forcible contact with any part of the helmet against any part of the defensive player’s body; or
(d) illegally launching into him. It is an illegal launch if a player (i) leaves both feet prior to contact to spring forward and upward into his opponent, and (ii) uses any part of his helmet to initiate forcible contact against any part of his opponent’s body. (This does not apply to contact against a runner, unless the runner is still considered to be a defenseless player, as defined in Article 9.)

Note: A player who initiates contact against such an opponent is responsible for avoiding an illegal act. A standard of strict liability applies for any contact against an opponent, even if his body position is in motion, and irrespective of any acts by him, such as ducking his head or curling up his body in anticipation of contact.

Penalty: For a crackback block: Loss of 15 yards.

https://operations.nfl.com/the-rules...rackback-block

W.T. Sherman is my favorite General. After all he did order Atlanta to be burned to the ground.