Holy crap. It looks like every single person in a 5 miles radius is at that one intersection. I can understand the cops having a bit of confusion when there are 300 people milling around on the same street. They handled the situation wrong, but if you and your partner got called out to a domestic incident of kids at a pool uninvited and found 300 people that you suddenly thought you had to control, I could imagine anyone being a bit overwhelmed. But wow, if you don't have enough information maybe that is the first thing you do, gather more information. Don't just go nuts on everything.
That said I would like to see what happened right when they arrived and what information they had to work with. It is tough from a shaky video from some kids phone to really know everything that went down. It is interesting how context gets thrown out the window as long as we have some video footage that shows something we immediately perceive as bad. Good thing our justice system requires different standards than internet judges.
Edit: have to add, to make sure it is clear, I think what the cop did with that girl was excessive and that kind of **** needs to stop. But it all has a beginning somewhere and seldom do we see the beginnings to these things. Usually it picks up when some one decides this would make a cool youtube video and pulls out their phone.