From what I've read, most of the teens were invited by another teen who lived in the community (including the one who was slammed to the ground for mouthing off to the cop). Apparently, some additional teens who were not invited showed up which is what prompted someone to call the police but when this particular officer arrived on scene he didn't attempt to distinguish between teens who were invited and teens who were not and instead just started subduing every black kid in sight.
That is not what happened. First there were more then a "few" uninvited teens. Many of them jumped over the fence. They were being aggressive the young children who were there. They were not heading the warnings of adults. There was more then one police office there and they weren't subduing everyone in site. This incident occurred because the "victim" in question was aggressive and unresponsive to the police officers commands. Yet that portion of the video "some how" didn't make it onto the main stream media.