Just his play. The steady regression says to me that whatever the injury is, playing on it is making it worse.
Marble is playing a new position this year. He isn't the greatest shooter, and its probably pretty hard for him to adjust not having the ball in his hands all the time. He is pretty crafty when he has the ball in his hands and can draw a lot of fouls. Marble just isn't one of the conferences superstar. He is a good player.