Legal Question in Family Law in Texas

No. Although he is 17, and cannot be termed a runaway; since there is a court order from the divorce which designates residence, you would be in violation of that court order. You should get a court order modifying that order - if your son will tell the judge that his stepfather is hitting him, it should not be a problem, particularly in light of his age. An attorney is the best route to take, however, if necessary, contact CPS in his jurisdiction; as they will likely place him in your care.