That is, how many cops do you need on hand to arrest one person? How many do you need when the neighborhood is up in arms against you?
After watching the video I posted yesterday and others just like it, you notice that no one is getting arrested. It's immediately obvious that given the anger of the crowds and the relative size of the two forces, the cops couldn't arrest anyone even if they wanted to without provoking a full-scale melee which they would lose.
Something else you see when you watch raw video from these riots is the hatred directed at the police. You get the feeling that the crowd is itching for a fight. They've been whipped up into a frenzy by years and years of propaganda. The narrative they've been fed was originally designed to keep them voting for Democrats*, but it's metastasized into something truly dangerous.
Do you suppose the mobs know when they become too big to control?
* - 4 years ago, when Vice President Biden told a group of blacks the Mitt Romney (!) wanted to put them all back in chains, it seemed funny. I know I had a laugh at Crazy Uncle Joe. Looking back on that, it wasn't funny at all. It was hideous.