The moment that Henry took a step forward, Sammy also reacted. He had already been anticipating any movements that were going to be made by the two people in front of him. So, the moment that Henry made a move, he believed that Henry was trying to force his way in.
But that was something that he was not going to allow. As long as he was alive, he was going to make sure that nobody managed to reach into that house and interact with Alex. That was the duty that he had been given by Alicia, and it had to be fulfilled.
He immediately raised the hammer that he was holding in his hand and swung it towards Henry. Of course, he did not utilize his full strength considering that until now, he had not detected any killing intent that came from Henry. That implied that Henry was not here with the intention of doing any harm.