I drove transit for 4 years. Looks like she hit first, so he has a right to defend himself. Although getting up outta the seat and clocking her as hard as he could is not going to fly with any transit agency ruling. Push her off the bus, close the door and wait for the cops. Don't let her back on, don't wander around trying to kick her *** some more.
I put up with plenty of abuse from passengers, but I never had anyone actually assault me. The way it works in that situation is trying to not escalate situations or jeopardize anyone's safety. I had one guy start flipping out, wanting to fight me, so I said, "OK, let's do this. But I can't fight you inside the bus, it's dangerous for others and I'll get fired. You want to fight, let's take it outside." The second he stepped out the door, I closed it and drove away. Problem solved, and nobody got hurt.
That driver will most likely be fired, because he didn't remain professional, and he endangered other passengers safety. It doesn't matter if "she had it coming", although that punch just might teach her to shut the hell up and get off the bus next time.
