Ambush.
Who didn’t see this coming. I’m just surprised they weren’t armed and shooting.
Dry run, that's for next time. Seriously, these are insurgents, they have trained for this apparently for a long time. Same with fireworks activity (to assess response, get complacency so when they do armed incursion there will be no rapid response), the "standard" riot gear (notice everyone has a skateboard (shield, weapon), who knew everyone was a skateboarder). This is a well planned, well organized Marxist insurgency.