I see 4 potential blocks in the back, although 2 of them look to be either good blocks or there isn't enough on the screen to determine if they are blocks in the back. 1st one is the one everyone is talking about, the one on the 30 in front of the HL. But from the original post, the play was replayed at the 30, so that can't be the one they worked from.

Second one I see is the one Ed found, at the 40 on the HL side. That has to be the one because of the location of the ensuing spot. However, I'll agree with Welpe that the camera doesn't show it very well to determine if it was a block in the back. One of those HTBT moments.

Third one looks like a block on the back, but because of the camera angle, it looks like a good block on the side, is around the 48 on the LJ side. It's the same defender that supposedly gets nailed in the back on the 45 (looks more like the 43) that refbuz was talking about. I would say either of those couldn't be it because of the ensuing spot after the penalty enforcement, and since TerpZebra said the referee said that the linesman threw the flag.

This play had penalty written all over it from the moment the reverse started, and really turned south on the offense penalty-wise the moment the flanker decided to reverse course and go the other way. As a former coach, I wouldn't have been shocked if just about EVERY official on the field had his flag down for something on that play.