You have never watched anyone fight. Need to be a closed fist to be a punch. There's no pull back, and Hulls did what he should have and flopped. He never even looked in the direction of Hulls.
1. Sure looked like a close fist to me.
2. Pretty sure there's a reason that jabs are useful in a fight (no pullback, meaning fast)
3. Hulls would have to be the world's best flopper. His head immediately jerked pretty hard, kind of like someone who just got punched in the jaw by a guy built like a brick **** house. Not a flop, IMO.
All that said, it was pretty clear that it wasn't intentional. If anything, it looked like Robinson was maybe hooked a little and forcefully broke free. Hulls was just in the wrong place at the wrong time.