Ok, now more in-depth on this play:
If you are the LJ and see the block and deem it legal, then see the flag by the R, what do you do?
I've had a similar situation happen. I had a really good and complete look at the block, and ruled it legal (in my mind). Another official threw on it, but I felt like he could not have possibly had a really good look at it. I approached him and told him that I had a really good look at it and the block started on the shoulder, and, as the blockee rotated toward the BC, the block migrated to the back. He replayed it in his mind, and realized that he probably didn't see the beginning of the block, so he withdrew the flag. I didn't tell him to do anything, and I didn't question what he saw. I offered the best information I could, and he made the decision to rescind.
That approach was learned from Tim Millis. If you have something to offer, offer. But don't ask, "What did you see?" His best example was (paraphrashing): Don't ask me if I thought it was catchable. Hell yeah, I thought it was catachble, or I wouldn't have thrown on it. If you think it wasn't catchable, just say so. Then I'll decide if I want to pick it up or stick with it.