A brawl broke out between two attendees of a Bernie Sanders rally in Colorado on Sunday evening.

The fight, which broke out while the presidential candidate was speaking at the Colorado Convention Center in Denver and was captured on video, happened after a Sanders supporter confronted another man wearing a T-shirt that said “Black Guns Matter.”

The man wearing the shirt, who is black, told KCNC he was recording the Sanders rally when the other man came up to him and called him a “racist.”

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“He had a problem with the shirt I was wearing,” the man, who did not identify himself to the channel, said. “I was recording the event, he walks up and calls me a racist. But I thought, ‘What’s he know about black lives, about discrimination, or, for that matter, the representation of the shirt.'”

The confrontation quickly escalated, with the fight spilling over a metal barrier and the two men falling onto the ground not far from the rally crowd.

Sanders did not respond to the scuffle and continued speaking.

The Sanders supporter, who identified himself as Tyler, told local media the confrontation escalated after he heard the man in the T-shirt booing Sanders.

The man in the shirt – who said he agrees with many of Sanders’ proposals, but not on guns – expressed shock at being attacked at a political rally.

“I think it’s really a sad thing at a Bernie rally, when someone has a difference of opinion, that someone would be treated like that,” he told KCNC. “I thought it really would be a lot more inclusive than that. It’s not a safe place to express differences.”

The man added: “I would expect that sort of thing at a Trump rally.”

The incident in Colorado is just the latest report of attacks on critics and political opponents by Sanders’ supporters, although this is the first report of a physical fight at a rally this cycle.

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On Monday, Michael Bloomberg – the billionaire former New York City mayor who is running for the nomination – tweeted out a video featuring aggressive and sometimes threatening tweets, texts and memes supposedly from Sanders supporters.

"Vote Bernie or bad things will happen," one message said.

"We know where you live. Where you work. Where you eat," said a string of messages.

"Libs who are flirting with Bloomberg now should be aware that they are going on lists," said one tweet. Several targeted other Democrats in the race, calling Sen. Elizabeth Warren, D-Mass., a "snake" and former South Bend, Ind., Mayor Pete Buttigieg "a demonic rat."

The video ends with an ironic use of a clip of Sanders saying, "It is vitally important for those of us who hold different views to be able to engage in a civil discourse."

"Really?" Bloomberg's video asks.

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Last week, the powerful Culinary Union Local 226 in Nevada released a statement claiming that its members had been “viciously attacked” by Sanders’ supporters after the union publicly warned its members against backing a candidate in the state’s caucuses who supported “Medicare-for-all.”

The union’s statement came amid reports of harassment of union members over the phone and on social media by alleged Sanders’ supporters less than a day after the union released a flyer claiming that Sanders wants to “end culinary healthcare.”

“It’s disappointing that Senator Sanders’ supporters have viciously attacked the Culinary Union and working families in Nevada simply because our union has provided facts on what certain healthcare proposals might do to take away the system of care we have built over 8 decades,” Geoconda Argüello-Kline, the secretary-treasurer of the Culinary Union Local 226, said in her statement.

Bethany Khan, the union’s communications director, has said that the union has continued to receive numerous attacks after it decided not to endorse a candidate in the 2020 election.

Fox News' Ronn Blitzer contributed to this report.