I kind of sympathize a bit with the man. He's probably from the old school when people could hit each other's kids and not be committing a crime or an offense one could be sued over. He probably didn't think too hard about it and just reacted.
But I am frankly astounded that so many people think he was justified or that it is okay for a stranger to use physical force on someone else's child. Like many have said, you can't go around slapping adults whose behavior is bad. Why is it okay to hit a random child whose behavior is bad? Children have rights to be free from a stranger assaulting them in the same way adults do.
And someone posted that until 20 or 30 years ago, physical discipline was okay. It's only now that it is becoming bad to hit children. Well physically "disciplining" one's wife was okay for thousands of years as well. Children used to be deemed the personal property of their parents and the parents could do whatever they wanted to with them. Children used to work alongside their parents all day in mines or fields, instead of going to school and that was okay. Just because it is historical does not make it right.
This is not about "coddling" children. There would have been nothing wrong with the man telling the child, "Hey! Do not touch my cat's carrier again. Do you hear me?" And then physically blocking him from getting near or even removing his hands from the cage. But hitting the child? It's simply not right.
I had a similar situation. I went to the vet with my very scared cats and a bunch of kids were running around right outside the door, banging on it and banging on the windows. All the animals inside were scared. I had no clue who the parents were and no one seemed to be stopping them except at one point, a lady who seemed unrelated. I asked the people at the counter to do something. They did not. I then went outside and said firmly, "Do not bang on the windows or doors again. Do you ever get scared at the doctors? Well, this is the doctor's office for the dogs and cats and they are scared. When you make noise, it makes it scarier for them." They stopped for a long time but then after a while, one of them tested me and yelled through the mail slot. The workers did not seem to care and did nothing. I went outside again and said, "Hey. What did I tell you? Stop making noise."
It was at that point that a parent surfaced and began apologizing and yelling at them.
I never went back to that vet, though. I feel they have an obligation to try to make things quieter and to control their clients. (That was not the only noise that day).
In any event, I never once thought about striking one of those kids. That's simply not appropriate.
So, should this guy be sued? Nah, I don't think he was malicious and he probably acted on instinct. Misguided yes, but mom made huge mistakes that day too. The mother should have controlled her kid. When that didn't work she should have taken him outside. Since she didn't and a stranger lost his cool, she should have said, "I'm very sorry for my child's behavior but it is not okay to hit someone else's kid." But, since she wasn't the type to control her child to begin with, of course she is the type to sue a man her child was harassing instead of walking away.
Final thought, I hate hearing how kids "need" a swat or that a lack of corporal punishment is creating monsters. No, it's a lack of parenting that creates monsters. I handled 12 preschoolers when I was a preschool teacher without hitting one and had them under control. How could I do that and a parent can't handle one without having to resort to physical punishment? Hitting is not necessary to get a kid to behave.
Also, go ask all the men in prison today if they were hit. Invariably, 99.9% were spanked, "whupped" or whatever. Inconsistency, apathy, laziness, and a lack of a backbone is what creates spoiled monsters, and neglect and abuse and poverty (and more rarely, spoiling) is what creates criminals, not sparing the rod. JMO.