Playground Etiquette

What exactly is proper etiquette at the playground, for both children and parents? I took Noah to the indoor playground at the Avenues Mall today so he could run around and hopefully make some new friends. We were literally there not even 30 seconds before a kid, much bigger than Noah, came running up behind and pushed him face first into the floor. Of course Noah, who spends most days indoors, was shocked and cried immediately. All the other kids, again much older than Noah, ignored him and ran around him screaming, which made him even more upset. The father of the boy who pushed Noah didn't get up from where he was sitting and just yelled across the playground at his son.

And that was it. 

Maybe it's none of my business, but I felt that this parent missed an opportunity to teach his son proper playground etiquette, especially around children who are much younger and smaller than him. Noah spent the next few minutes clinging to me, not wanting me to let him go. I took him down the slide a couple times and sat with him while he watched the other children play, just so he could feel comfortable enough to start walking around again. A few minutes later, he seemed ready to play again so I set him down. And the same kid came running around and pushed Noah down...AGAIN! At this point, I was highly upset and annoyed and actually encouraged Noah to cry louder, instead of trying to shush him, just so the other parent could hear and oh, I dunno, maybe actually get up and discipline his kid?! Which brings me to my original question: what exactly is proper etiquette at the playground? Especially when it comes to discipling someone else's kid? I wanted to scold this kid myself, for pushing down my son, but I wasn't sure if I'd be overstepping any boundaries. John absolutely thinks I had the right to yell at this kid, but I'm still not so sure. What do you guys think? In the end, I didn't have to worry because the other parent eventually scolded his kid (albeit from his seat without getting up) and made his son apologize to my son. He came over looking quite sheepish and said he was sorry to Noah (which leads me to believe that this kid was at least old enough to know not to push over a much younger kid to begin with, but I digress). Noah just looked at him blankly, but I'm sure he forgave him. At that point, however, he was so over the playground so we left and got some ice cream instead.