What makes you say that her dog was "vicious"?
Are you guys kidding? The OPs dog attacked this guys dog and he was defending it. If some dumb pitbull attacked my dog for no reason I would kill it if I had to. Pitts are dangerous and bad Pitt owners are also dangerous. The op sounds like a good owner who made a mistake and she was right that the man defending his dog was in the right.
I'm sure the punch barely hurt the Pitt.
Pitts are dangerous? That's an uninformed, breedist statement. Did you know that Pitts used to be called nanny dogs because they were often used to take care of children? Did you know that a couple of years ago the "dangerous" dog de jour was the Doberman? Before that Rottweiler? People are dangerous. People mess up some dogs and we blame the dogs. Dogs are the most domesticated animal there is. All that a dog wants to do in the world is make their people happy. It is that eagerness to please that bad people exploit.