Before I answer, please understand, I'm very sorry you are going through this. I know how tough it is to be estranged from one's child.If a teen is violent, and neither parent can do anything, then just what do you suggest could be done? Not doing anything for consequences only makes things worse.
When he hit me at his mom's house back when he was 16, he was the man in charge, mom had lost control of him. Whatever rules she put before him, he disregarded. The two of them live in a 6 bed McMansion, and he had no chores to do. She even had a lawn service mow the grass, with a teenage boy and a riding mower sitting in the shed!!
When he lived with me, he had chores to do at home. When he misbehaved, I did confiscate his phone, made him take the bus to school, took away his car, and grounded him at different times. I took him to counseling, paid for a Summer Adventure Bound Intervention Camp, met with teachers, etc.
He had consequences living with me. With his mom, she would tell and threaten him, the next day it was forgotten. I think he was so used to having his mom roll over to him that he thought he could do that to me, as well. Two weeks after he was arrested for assaulting me, he drove almost 90 miles to my house to get his things. Why did his mom still allow him to drive?
He told me that living at his mom's house, he went to a park and was held up at gunpoint while trying to score drugs. I wanted him out of that environment for his safety.
So you were injured when your boy was 2? But he didn't punch you until he was 16? When did his Mom split up with you? How old was he? And again, why did you settle for seeing him only every other weekend? Trust me, I get that you got a raw shake on the way that his Mom raised him. I'm living that right now and that's tough.
I don't believe you can look at these things in a vacuum. What would I have done if he clocked me? Probably physically grab him and put the fear of God into him, I guess. I'd def respond in some manner, but not by calling the cops. That doesn't mean that you weren't trying to right by him and you...I just wouldn't have handled it that way.