What happens to an adult if he refuses to comply with the law?
The police will hit him if resisting.
In order to arrest a person who is temporarily violent, or out of his mind, fueled by alcohol, or anger, there is no other way. When I taught, I once had to use force on a child who swinging a floor hockey stick at his classmate's head. (restraint) But this isn't corporal punishment. It's necessary to protect society. Once that person is behind bars, it's against the law for the police or jail guards to go beat him.