Okay, 0:34 seconds in, you can hear the cop say "I tell you to stop, you tell everybody to keep going?!"
That adds some context. The cop attempted to stop them, and they tried to run.
Like it or not, skateboarding ordnances exist because we have a lawsuit happy society. If little Jimmy fractures his skull because he tried to tail-slide a 9 foot rail, his parents can sue the city and win. That's a whole different topic for another day though.
The first kids "chokehold" is anything but. You hear no coughing, gagging, or spluttering. There's no gasp of breath when he lets him go. He had knee to belly control and could have very easily beat this kid senseless. He didn't bother with any of the other dozens (and far more painful) chokes or even a joint lock. He could've just mounted him, rolled him over, and then handcuffed him. He didn't do any of that. He actually took all of the pressure off of him and went back to verbal commands. You can tell from his leg positions and grips that the cop at least has a rudimentary grasp of grappling.
After he'd already ordered them to stop the first time, they're all resisting arrest with their non-compliance. That's why you don't argue with cops, even if it's something minor. The second kid, I can only speculate since I wasn't there... was probably part of the original group asked to stop, and beat cheeks away after he told the cop he had a picture. The girl tried to run when ordered to sit, and was detained for it. The fourth kid stepped into the officer after he detained the girl, and got himself arrested.
I'm willing to bet y'all if the kids hadn't acted like *******s and run to begin with, none of this would've happened. It's silly to act like this is some violent act of aggression on behalf of police against skateboarding kids. He told them to stop, they ran. Pretty simple.
And I don't even like the police. I've been detained and handcuffed on the hood of my car 4 times without ever once being arrested. Friends that tried to run.. well, they went to jail.