Snitches get stitches.
Not that I encourage this, but if you go out and try to get someone in trouble, sent to jail, foster care, away from their family, etc...how do you not expect this to happen? If you try to take someone's freedom away, this is what happens next time they see you. Of course they shouldn't be selling drugs, and I'm not saying he should have kept it to himself either, just saying when you put the two together, and then you cross paths, this happens.
Also, I'm sorry but the beating is not that brutal. I got jumped a few times in high school by grown ass manchilds, and one of the times was almost the same thing, a teacher saw it happen and just watched until the beating stopped, and then came to my aid and took me to the office. I didn't expect him to step in and potentially face a lawsuit from the kids' parents, and didn't expect this bus driver to, either.