The level of play (and practice) each and every night is way more physical than high school/AAU. Going to school, training, classes, away game travel, living away from your old support network and finding a new one. How to fit into a team when you are used to being "the man". Maybe being a more vocal and on-court leader is part of what this year is as well. All things a young guy is grappling with. It all takes a physical and mental toll. He'll grow from it, though. He probably also dominated most nights in AAU, whereas guys may not be as gifted physically but they know how to play the game better and make him work harder. It's not abnormal for this to happen to a freshman. Same goes for rookies in the NBA.
I would agree he seems pretty calm out there and doesn't get very jacked-up. I still think at this point we should just feed him the ball more and see where that can take us. Nothing else is really working at this time.