Riley Burt felt. He felt that Mahe showed preference for the Poly backs (Fonua & Tolutau) over the black backs (Canada, Hall, Dye, himself). His fallings out with Mahe are why he moved over to the defense for a while.
By the way, this is based on my reading of the tea leaves from Twitter and message boards, not from insider knowledge. I hope it's wrong.
In my final analysis of the situation, Hall was our best RB. I hope it was strictly health that kept him from being the feature back all year long. Canada was #2. Burt was #3 and should have played much more. Fonua showed promise as a bruising runner and it's a shame he got hurt, but he was not a threat to break a game open. After we lost Francis Bernard to his tomfoolery, Fonua should have been moved back to OLB during fall camp imho.