Even before the pick six, heaps got drilled by a blitzing LB. I think it was in the 2nd or 3rd offensive series. It wasn't a sack. He'd gotten the pass away, but, got knocked down very hard. You could tell he had NO idea the guy was coming.
I recall a close up they did on Heaps' face right after that play and I could see alarm in his eyes. I noticed that after that he was skittish in the pocket. That's when he really started to under/overthrow receivers. (He didn't do it as much his freshman year as he did in his Sophomore year.)
I think it was a mental block he couldn't get over. It led to hurrying throws, locking onto a receiver (hoping the guy will get open soon so he could throw the ball and remove the target on his back). I know he was knocked down plenty his Freshman year, etc., but, i remember distinctly thinking after that first Ole Miss hit that something got into his mind and he never lost it.
MHO only, of course.