There are ways of dealing with kids that do not escalate the situation.
I’m a teacher, and only once or twice have I had to get physical and that was during a fracas where another student would have been seriously hurt.
I’ve had plenty of kids disobey me, or even (once or twice) insult me, but the way to “lose” in front of the kids is to lose it in front of the kids. I’ve always ended up mainting order but having the respect of the kids.
You play the long game, not the win-at-all-costs-in-the-now game.
That involves getting to know the kids and advocating for them.
Those cops didn’t prove they were in the right, they proved they could beat up a girl.
Given the girl’s situation a decent cop would have let her phone her dad from his office (the cops in our schools have their own office) and probably would have got her a drink of water too.
How would he have known this was the right thing to do? Because he would have asked questions and engaged her in conversation.
BTW I’ve taught gang and street kids kids and stopped fights between scores and even hundreds of kids, so I have experience.