Linky link to the video.
I've watched the video a few times, and the summary above isn't quite an accurate representation of what you see on it.
The bully looks to be three or four years older than the vicitm and is easily twice his size. He repeatedly makes a finger gun next to the kid, making a comment, then slaps the smaller boy, sometimes just hitting him. A second boy the same size is there not getting violent, but seems to be a part of the tuanting based on his body language. To his credit, the smaller boy doesn't just take it, but defends himself each time. Eventually the larger boy stands up and begins beating the smaller one. Brutal isn't a bad description. The bus driver yells at the boy to stop, telling him that he's "off the bus" and that it's "all on tape". The time stamp shows the bullies being removed from the bus five minutes later.
My commentary:
It's an assault by a boy backed up by another, both twice the size of the victim.
The bus driver intervened immediately and the assault stopped. I see no place to fault her for her behavior.
~
I was often the target of social ostracism in high school, but never any physical bullying. Girls go after each other, but we do it with psychological warfare rather than physical combat.
Gilda