Just remembered there were two sort of incidents. When I first got there a municipal garage across the street was letting out some Denver PD SWAT vehicles, the first being a ridiculously heavy armored one with cosplayers hanging off of it. A few folks blocked them for a few seconds, but left before they could be shooed. The vehicles all left then, must have been off to do some other shitty operation. There was one driver stopped by the march at a cross street trying to push through, but a volunteer in a vest stood in front basically daring him to give it gas while photographing the plates and another volunteer recorded him.
Hightlight interaction was in the burbs though when a guy drove by slow shouting profanities at the crowd and one woman just belted out super, super loud "We love you!" Dude did not have a response.