From what people were saying and the switch to defense and FG team was indicative of the coaches lack of confidence of his grasp of the game.
Defensive line is much less complicated because you just line up and go to a hole or occupy a gap or just control two gaps.
Offense is much more difficult because of so many changes by the defense and different blocking assignments for each play.
I think it was less of his ability and more of his lack of understanding Ms passion for the game. The medical retirement allowed him to keep his scholarship while freeing up a scholarship.