Watch in slow motion on this view. The Ute DB has the BYU receivers arm locked and begins to drive his legs into the BYU reciever toward the sideline and the reciever reacts by pulling the reciever down. The contact was initiated by the db and he was holding the reciever. You are completely blind if you can't see that on this angle. Had the reciever not been held, he could have come back to the ball to make a catch.
THE PAC 12 REFS ABSOLUTELY LET UTAH GET AWAY WITH MUGGING BYU'S RECIEVERS THAT GAME.