Witnessed the whole thing. I don't know why he decided to run towards the punter. If he had stayed left he had three blockers in front of him and probably would have went for a TD. I don't think he intentionally tried to kick the punter. I think it he simply timed his jump incorrectly and he probably thought the punter was going to dive at him. Regardless, he will receive a heavy fine from the NFL.
Looks ta me like the punter was falling to his knees to give Antonio a low block, perhaps to take out his legs, Antonio tried to jump over the punter and when he saw he wasn't going to clear and would probably suffer the knee or lower injury the punter intended to deliver, so he did what he had to do to give his leg somewhere to go to land squarely after contact. Watch the video and you can see Browns leg would have been seriously twisted and probably be broke if he had landed on the punter who was falling in front of him, not towards him as a MAN throwing a block would do. I call for a fine and suspension on the punter for trying to injure a Steeler by making a pussy block.
#5 has his hand going for Antonio's leg in an attempt to break or sprain same, Good thing Antonio kicked his way out going for the target that would hurt the punter the least.