My kid beat your kid up

I took Adrien to the mall today. Big surprise, I know. But it's an indoor playground and it's already been 100 degree here for a month (at least).

His favorite thing to play on there is this little car. It seats about 3 kids. Adrien climbed in with two other kids and automatically this little girl who was probably around 3 or 4 years old starts being really nasty and telling him to get out. He kept playing and just said "no." Somewhere around five minutes later the little girl is on top of the car's hood and Adrien is inside the car. She's STILL telling him to get out -- with her face being about a centimeter from his. I was looking around for her parents. I mean -- intervention, please? Adrien was tolerating it so I didn't step in. I was really waiting for this little brat's parents to do something. I finally figured out that she was there with who I'm assuming is her grandpa.

Finally Adrien got tired of her being in his face and he hauled off and punched her. Straight in the nose. She backed off. I was kind of astonished -- he usually doesn't hit unless he's just playing too rough and gets really excited. Rarely does he hit out of anger, and generally when a kid's being mean to him he just moves on to something else. I immediately rushed over, but before I could even get there the little girl was already looking at me and in a whiny tone she was all like "He punched me..." I just looked at her and said simply "You were being mean too." Then I got Adrien and we left the play area.

During this little conflict, I noticed her grandpa looking at me all like "Look what your kid just did!" I'm sorry, but I have no sympathy for her. She'd been antagonizing him for a good five to seven minutes. I wanted to punch her myself long before Adrien did. And on top of it, had her grandpa stepped in and told her to play nicer, Adrien wouldn't have been pushed over the edge.

As much as I feel like hitting is wrong, I feel like he was justified in it. She'd been nagging at him and taunting him for quite a while -- imagine how long 5 minutes is to a two year old. She's probably almost twice his age. I didn't know what to do besides leave the play area. I didn't want to not do something about his behavior...but at the same time I hate punishing him for defending himself. After all, she was being a real bitch.

What would you do? How do you feel about your kids sticking up for themselves?