do you support teachers who beat up students?

No, anyone ever laid a hand on my child they better watch out. I would go out of my way to destroy their career, they are supposed to teach and care for the children, they have no idea why a child behaves the way it does and negative reinforcement of any kind let alone physical abuse has been proven to stunt a child's development.
Talk to the kid, if you believe they are just testing boundaries then detention is there for reason.