I learned something tonight about pro football rules. If you commit a personal foul while committing pass interference, that is the only situation where the refs can assess a double penalty. Tonight, the defender grabbed the receiver's face mask to draw both the pass interference foul and the personal foul on the same play. So, the refs marked off the penalty first to the spot where the pass interference occurred and then added another 15 yards on top of that for the same act of grabbing the face mask. In this case, it was a 28 yard penalty in total.