Douglas had figured that he would be deserving a lashing from the family, so had not defended himself as he saw the father's leap.  He took the hit in his jaw.  Ben had a strong punch and Douglas stepped back a few paces but didn't fall.  He was a strong man himself and knows how to give a good fight himself, should he wish to.  Though he did not do so at this time.  He had been in the wrong and knew it, despite the episode was not his fault.  He should have somehow have protected the lass.  He stood there expecting more punches.