The kids are riding willingly past a cop car.

A safer thing to do is block the road with cars and kettle from behind. Then even if people flee on foot you can impound the bikes or whatever to a vastly better effect in terms of reducing public nuisance.

The officer here wasn't improving safety, he was making a larger hazard, putting himself in danger, and ended up paying for it.

They want to use their toys and they want to cause harm.