The South Carolina teen brutalized by cop in viral video was reportedly in foster care, having been recently orphaned. That may go a long way toward explaining her acting out. Nothing explains or excuses the fact that a policeman was called into a classroom over a cell phone stand-off, nor does it explain or excuse the policeman's illegal conduct.
If you question that, you should question why you do, because it tramples on the Constitution. I hope she gets relief in the courts, bratty behavior notwithstanding. (And that's what we're talking about here, is a bratty flair-up. It's not like she's threatening to blow the place sky-high or physically menacing anyone.)