The physical abuse was too much, Fletcher was too smart for that
Obviously there are physically abusive teachers and coaches and I get they were just showing how intense Fletcher was, but I think that made him look dumb when he was otherwise brilliant. Fletcher had to know all it takes is one kid telling a parent or teacher that he was slapping a student in the face repeatedly to get him fired, if not arrested. He was good enough with his emotional and mental abuse. Assault is too reckless for him.
Throwing the chair was especially too much. What if that his Andrew? That would leave extreme injuries. The slapping he could maybe deny since any mark would fade quickly, but a chair to the face? Concussion, broken teeth, messed up eye? No way to hide it. Fletcher would literally go to prison