The short answer to this question is Dink Meeker. Dink is a toon leader in Rat Army. He is the primary reason for Rat's success, and he asked for Ender. He trains his toon separately from the rest of the army in practice sessions, and essentially, he does whatever he wants. All Rose knows is that his army is winning and that Dink has something to do with it. Rose comes across as threatening, but in reality, he is a weak character who is merely hiding his insecurity through a fake personality of being laid back, somewhat lazy, and funny. According to Dink Rose "isn't some magic Israeli general who can win no matter what. He doesn't know why anybody wins or loses" (108).
Rose attempts on a few occasions to limit Ender's power, and to pick on him in front of the other boys, but despite these attempts, Ender (in Dink's toon) continues to be successful. In the face of winning, Rose eventually just leaves him alone.