The kid was a brat, but the teacher should have restrained himself from physically touching the boy. They were close if the video, I wonder if the boy touched him first, regardless the teacher should have just reported the incident. Back in grade school, the nuns/teachers used to hit some of the kids. I was never hit, but my mother always said that if they did hit me, it's probably because I deserved it. Most parents didn't have a problem with it, there was no real abuse.
That boy should have been brought up better by his mother, and never said such a thing to a teacher in charge (or anyone for that matter). In this case, the takedown also looked pretty mild to me, calling it a body slam IMO is just overkill. With the mother making such a fuss and wanting to sue over something so minor, the boy's future violations will probably escalate when he reaches adulthood. I dunno, mixed feeling on this one.