Once again Football is a privilege with set requirements one being to listen to your coaches. The kid was asked to not wear them that should have been more than enough to send a clear cut message.
The coach has discretion on what payers can and cannot wear. I know one of my old football couches was a really big stickler on everyone being uniform, especially for games. However, this couch should have handled this better. Kicking the player off the team was a little extreme.