It looked like he was lining up as a defensive end on that play.
Nice title to the thread.
I believe you are correct. He had been double teamed on the inside and it looked like we were dialing up a blitz. Hageman had been getting the "push" on the guard all game and being frustrated by that, he put his hands to his face. Getting a sack without your helmet is highlight material. Epic!
It was interesting that during the A&M vs Bama game (I think it was that game - I was tired and they were blending together) that a player was flagged for continuing to play without his helmet. He was also a D lineman that had his helmet pushed off by an O lineman, and he went and made the tackle and was flagged for illegal participation. I believe it was a 15 yard penalty? Not sure on the rules but either way I'm glad Hageman wasn't flagged for it! That was AWESOME!