Well, it started as a peaceful anti-police brutality protest. People unaffiliated with that protest then started getting raucous and a mob mentality took over, it seems.
It's hard to understand from a cultured perspective, but is actually a pretty fundamental animal aspect of humanity. Kinda a fight or flight reaction being triggered by other peoples' fight or flight reactions, even though you are not aware of what the actual danger is. And in the context of a mob, you are far more likely to choose fight (as you begin to comprehend others as your "allies" in the situation, and there's minimal risk inherent in being an aggressor when the riot begins).
There are a lot of human quirks that really only start appearing in groups, and the people in them aren't really aware of how their behaviors change.
For example, take a busy building in which everyone is trying to get in or out. The fastest way to get everyone through is an efficient single-file line (or lines). But as the crowd grows, instinct urges you to get to your destination faster. So you start rushing more and more, getting closer to each other than you would ever wish to do normally (especially since Western culture generally defines personal space to be a very wide area). Eventually, that turns into real pushing, and you need to really fight to get through the door (though not in a literal sense).
It's even worse in instances where you perceive an actual benefit in getting there faster, like when boarding a bus or train.
Anyways, you all are horrible, @#%^ed up people
Never underestimate the healing power of a massive dong.