How and why does Miles become injured during the "triple-date" that Alaska has arranged in "eighty-seven days before"?

The triple date turns out to be another basketball game. As the game progresses, Chip continues his routine of harassing the opposition. At one point, the particular player he's attacking moves menacingly towards the group, and Takumi and Miles run, Miles being knocked to the ground by the basketball fired at him by the angry player.