From what I saw, he did one too many snap rolls on the downward 45. This could have been caused by any number of things:

1. Misjudged his altitude entering the maneuver. This happens occasionally, as in the case of the Thunderbird pilot who crashed in Idaho in 2003.  However, given that Jim Leroy had performed earlier in the day, that is not likely the case.

2. His view was obstructed by the smoke/haze. There were 2 aircraft performing at the time, both were using smoke. It wasn't clearing very quickly, and this could have interfered with his view.

3. In an effort to perform on the edge, he may have been trying to give the crowd a more dramatic performance, pushing the envelope just a little farther than necessary.

4. There is always the remote possibility that vertigo or spatial disorientation played a role. Also, mechanical problems are a possibility, though I'm not inclined to believe that.

From my vantage point (it happened right in front of me), he was doing downward snap rolls, and as he exited the last one, he leveled his wings and was trying to pull up. His downward momentum and lack of altitude prevented this from happening. He hit the runway at a high AOA and high rate of descent.

 My best wishes to his family.