I would assume that, like others have mentioned, the B would have this call, and I agree that whether or not the foul affected the play, it was a safety concern which should get called.
On a slightly different subject-but being an umpire, I notice these things- The U seems to be lined up awfully close to the line of scrimmage on this play. Not saying that the play from the original post would be his call, and even if he was lined up deeper, he would not have been able to see that action, but I do think from that close in, he would miss a lot of what he should see. Not to mention putting himself in position to either get rolled or hit from behind as the LB is pursuing the action. It almost looks like he impedes the LB from getting to the play where he is positioned.
Is that a normal positioning for crews in that area? I could see if it was 4th qtr and the Offense was going to take a knee, so that he could get into mixed colors quickly to stop the cheap stuff from happening, but this play occurred in the 1st qtr. Why be up so close?