We've seen these euphemistically labeled "flash mobs" in Chicago, Philadelphia, Milwaukee and Montgomery County Maryland. These jurisdictions are generally considered less accommodating of citizen self protection using handguns.
I haven't seen any reports of violent mobs in Kentucky.
By the way, it's not me describing these things as racially motivated. One of the attackers at the Wisconsin State Fair is being charged with a hate crime.
Of course the riots in England were perpetrated against a population that has been completely disarmed.
And the police just stood around for the first couple days. Read up on the current state of policing in England, it's an eye-opener. Retired prison physician Theodore Dalrymple (Anthony Daniels) has been writing on the subject for 20 years and is probably as good a place to start as any.
Some of the English self-defense cases are just plain ridiculous, Here's one from last year via the Telegraph:
Myleene Klass, the broadcaster and model, brandished a knife at youths who broke into her garden – but has been warned by police that she may have acted illegally.