This is from the Big XII bulletin, Aug 27, 2013:
Blocking Below the Waist
Understanding that this rule underwent a few modifications and editions during the spring, even with the addition in June of the crackback provision, the general theme that the Rules Committee is trying to promote is to gauge actions in this area based upon the block rather than a geographic reference. There are three exceptions to this theme: close line blocks within the Low Block Zone, Crackback blocks, and Peel Back blocks, but even these have guidelines. A Crackback block is no longer defined as in previous years and is intended to apply to the player who immediately after the snap moves in toward the original position of the ball and blocks low. The original position of the ball is an area and we no longer have that 120-yard line running the entire length of the field; but, there is also no distance requirement and you can have an illegal crackback block by a very wide player who goes after the snap inside a considerable distance and blocks a defender low, even if from the front. The key is that we all understand what the crackback block is and is not. At some point during the play, there is an implied transition to the 10-2 concept of blocks even for players who immediately after the snap are prohibited from going inside to block low, provided they are not in route to the inside to make low contact as this transition occurs. It is impossible to write a rule that dictates exactly when this transition occurs, but as a general guideline, once the ball is clearly outside the low block zone and originally restricted players stop their movement toward the inside, that is a good reference to then just focus on the block itself being in the 10-2 frame and not a Peel Back toward their own goal line. Again, this is not absolute as you can certainly have an illegal crackback by a wide receiver who is at the snap on the move toward the original position of the ball and blocks low even though the ball has moved outside the zone; that would still be illegal. Another reference that the Rules Committee also intended is to consider whether or not the defender has a reasonable opportunity to see the block coming or to protect himself. Well after a play develops, low blocks clearly from the front where defenders have plenty of time to protect themselves are not intended to be illegal unless they are Peel Back in nature. Review again the various examples of plays that we have discussed and we will continue to provide additional examples as the season unfolds.
