Play video content EXCLUSIVE TMZ.com

Anti-Trump protests are already getting violent -- we got this crazy video of a fight breaking out on a Washington, D.C. street, and a woman was assaulted ... just one block from the inauguration.

It's unclear what sparked the conflict, but it appears some Trump protesters pissed off a group of men walking past them ... then all hell broke loose. Radio host Alex Jones was nearby and shouted for cops as one of the men hit a female protester.

Officers responded quickly, but it's obvious it's going to be a tense day in Washington. We're already seeing roving groups of masked people destroying property.