I have a problem when entering a player with ADHD

There is a child in my High School D & D group with A.D.H.D and he has a lot of trouble sitting still and distracts the other players. He is having a lot of fun and does not seem very interested in playing, but he insists that he wants to play.

I have considered asking him to stop playing for a while so that the other players can learn the game and help him more, but I think that could scare him away. He is a good boy and does not have many friends, but he is preventing other people from playing the game. I have seen him get up from his chair and literally start to fight with one of the other players. That I have to do?