Crack Back Block

[seanireland]

Originally posted by andy1033
This is an illegal shift if the split end is not 5 yards behind LOS at the snap.

Agreed, but it seems he moved toward the defender at the snap.

As far as "what constitutes an illegal crack back block?" The answer is whatever constitutes an illegal block, period. Let us not forget that a legal block is described in 2-3-1 through 2-3-10 inclusive. The fact that the defender doesn't see the block coming has no bearing. The block just has to be legal.