This is a video of a school cop grabbing an African-American teenager by the throat for, it appears, trying to walk away. There had been a fight, the officer was telling him something, and the boy was trying to leave.
Unless the boy was making some kind of threat, which no one has claimed he has, there’s no justification other than raw assertion of power for this action.
The police officer needs to be disciplined. But won’t be. He’ll use lack of compliance as a justification for whatever action followed.