2012 rule changes
The NFL has added to the list of situations where a player is deemed “defenseless” as it pertains to certain hard hits. The rule protects defenseless players from a helmet-to-helmet hit, from being “stuffed” by an attacking player lowering his head, and from launching-type hits from an opponent.
Generally, the ball carrier who is under his own power is considered to be fair game for helmet-to-helmet hits, because the runner can easily avoid or induce the contact. However, defenseless players cannot avoid that contact, and those hits not only are subject to a 15-yard penalty, but invariably are subject to a fine no lower than $21,000.
The league added a player involved in a crackback block is a defenseless player. A crackback block usually administered by a player lined up as a receiver, who turns in to engage in a block rather than run a pass route. As the defender is unaware that the receiver has become an active blocker, these tend to be surprise blocks, and thus the defender has no way of protecting himself.
The video shows an illegal crackback by aiming low at the knees; the new expanded rule now makes a helmet or launching hit illegal as well. Legal crackback blocks can still be made between the helmet and the knees as long as it is not in the back.
Defenseless players who are protected from dangerous hard hits include the following, from the Rule 12, Section 2, Article 7(a):
(1) A player in the act of or just after throwing a pass;
(2) A receiver attempting to catch a pass; or who has completed a catch and has not had time to protect himself or has not clearly become a runner…
(3) A runner already in the grasp of a tackler and whose forward progress has been stopped;
(4) A kickoff or punt returner attempting to field a kick in the air;
(5) A player on the ground;
(6) A kicker/punter during the kick or during the return…
(7) A quarterback at any time after a change of possession…
(8) A player who receives a “blindside” block when the blocker is moving toward or parallel to his own end line and approaches the opponent from behind or from the side, and
(9) A player who is protected from an illegal crackback block.
Item 8 was also revised to add the words “or parellel to.”