Pops, you were a tough kid. I know about tough kids; I've dealt with literally hundreds of them. The kid in this video is not a tough kid. He may be, probably is, an obnoxious little sob, but he was completely passive in this video clip. No restraint necessary.
I just don't agree that knowing what led up to this assault would offer mitigating circumstances. Unless he'd committed a grievous assault, which all concerned admit he had not done, then whatever he did did not and could not justify what she did. And yes, I do know what I'm talking about. Like others on this forum, I've been there, done that, and have T shirts in every color!
I also don't agree that the school should be held blameless. Those kids were put in that room with nothing to do and no adult in charge. Of course they should have behaved properly, but both experience and common sense ought to have proclaimed that they wouldn't. People who run schools have no business indulging in magical thinking.