Occupy Wall Street drew its largest number of protesters to date yesterday, and the protest went without conflict. At least until the sun went down, that is.

By 9 p.m., most labor unions had called it a night, but several protesters elected to continue the march on Wall Street. To put it simply, things got out of hand between protesters and the NYPD. Occupy Wall Street reports that at least 20 protesters were arrested following a standoff with police, and this NYPD lieutenant was filmed using his nightstick against protesters.

This is the first reported incident of its kind at the occupation, but it wasn’t just protesters that felt the felt the wrath of police. Apparently, Fox 5 reporter Dick Brennan was on the receiving end of a nightstick as police swung for the fences, while photographer Roy Isen was maced.

The day was largely peaceful, but nobody expected an estimated 20,000 people to convene without there being a few fireworks.

[via Gawker]