It is not clear what prompted the escalation but the video does capture the tension at such confrontations. The officer appears to be ordering the suspect to do something just before the escalation. The officer throws the suspect to the ground either when he jerks or fails to respond to a command. It also shows how video cameras have changed the environment for police operations, (as discussed) which is why some prosecutors and police have worked hard to try to punish citizens who videotape officers in public.
I have been unable to find out what the young man was charged with after this arrest.