This is her stepdad. Listen to the tone of his voice at the beginning. He is getting off on her helplessness, and on his own control of her. He does stop himself, but there is still something very inappropriate going on with him, and I am _extremely_ concerned about what goes on in this household when the cameras are off.
This is not an acceptable way to discipline your children, and especially not your adolescent stepdaughter. This man had no business putting his hands on her like that, and I hope to God that her dad is still in the picture and will take appropriate steps.