When I clicked on this, I expected to see a child, reading some of the posts! Instead I see a man as old as 20 or so!
I also didn't see any body slamming.
What I saw was a young man without a valid ticket, giving it some gob, effing and blinding. I saw him being asked to leave and refusing to. I saw them try to escort him off the train and him resisting and I saw them falling over in the struggle that he caused by trying to stop them from removing him from the train. I didn't see any intentional 'body slamming'. I saw them tripping over one another and falling. And then trying to stop him from getting back on the train.
Everything that happened was a result of this young man's actions. Not child. Young man.
He didn't have a valid ticket. He was mouthing off. He refused an opportunity to pay. He started swearing. He struggled with the people trying to remove him from the train. He threw himself at them several times trying to get back on.
He could have been polite, he could have paid, he could have walked calmly from the train when asked to.
He chose to behave like that. He has to take some responsibility for what happened.
Like I say, I didn't see 'body slamming'. If it looked like that, as in wrestling body slamming moves, then I'd say hell yes, that's assault. But it truly looked to me like falling over due to this young man struggling and lashing out. They tripped over him because he was throwing himself all over the place instead of walking off the train when asked to.
He behaved disgustingly.
That said, they did the wrong thing. Once it became obvious that he was not going to leave the train voluntarily and he would need to be physically removed, they should have called the police to come and deal with it.