Anyone else would have realized that Cassidy was just trying to rile Elliot up to get him to hit him. In fact, the people sitting around probably did realize that. They also probably realized that hey getting in a fight while already being held for possible disciplinary action was a bad idea but. Hey. This was Elliot.

Instead he just tried to take a swing at Cassidy, because fuck that he's not that small to get stuck in the bleachers. Even if he basically did earlier.