Authorities said one male demonstrator was stabbed multiple times near the intersection of New York Avenue and 11th Street, and sustained injuries that were not considered life threatening. It was not immediately clear which side he was on.
Daily Caller contributor Matthew Miller shared what he described as an "all out brawl between Proud Boys and Antifa in the streets."
The Proud Boys is a conservative group known for occasional brawls in other cities, including at least once in New York City and at several demonstrations with Antifa members on the West Coast. One of the group's leaders was stabbed during another protest in Washington during post-Election Day demonstrations.
People wearing the group's colors, black and yellow, cropped up in numerous photographs and videos from the demonstrations.
The video from Miller showed two groups trading blows in an intersection as onlookers chanted profanities.
City police said they’d made at least 20 arrests – three of which involved assaults – but a total count wasn’t expected until Sunday morning. At least two police officers were injured and authorities confiscated seven firearms, according to a city spokeswoman.
They closed off streets and part of Washington's downtown, already home to boarded up stores and offices.
In some places, police physically stood between groups of Trump supporters and counter protesters, chanting or carrying signs and banners emblazoned with Antifa and Black Lives Matter slogans, to keep them separated.