– Last weekend, when a 27-year-old bike messenger showed up at the “Unite the Right” rally in Charlottesville, Va., he was ready for battle. He joined a human chain and linked arms with others, blocking waves of white supremacists — some in Nazi regalia — from entering.

“As soon as they got close,” said the young man, who declined to give his name and goes by Frank Sabaté after the famous Spanish anarchist, “they started swinging clubs, fists, shields. I’m not embarrassed to say that we were not shy in defending ourselves.”

Sabaté is an adherent of a controversial force on the left known as antifa. The term, a contraction of the word “anti-fascist,” describes the loose affiliation of radical activists who have surfaced in recent months at events around the country and have openly scuffled with white supremacists, right-wing extremists and, in some cases, ordinary supporters of President Donald Trump. They have sparred with their conservative opponents at political rallies and college campus speaking engagements, arguing that one crucial way to combat the far right is confrontation.

Members of antifa have shown no qualms about using their fists, sticks or canisters of pepper spray to meet an array of right-wing antagonists whom they call a fascist threat to U.S. democracy.

“People are starting to understand that neo-Nazis don’t care if you’re quiet, you’re peaceful,” said Emily Rose Nauert, a 20-year-old antifa member who became a symbol of the movement in April when a white nationalist leader punched her in the face during a melee near the University of California, Berkeley.

“You need violence in order to protect nonviolence,” she said. “That’s what’s very obviously necessary right now.”

Others on the left disagree, saying antifa’s methods harm the fight against extremism and have allowed Trump to argue that the two sides are equivalent. These critics point to peaceful disobedience during the civil rights era, when mass marches and lunch-counter protests in the South eroded the legal enshrinement of discrimination.

“We’re against violence, just straight up,” said Heidi Beirich of the Southern Poverty Law Center’s Intelligence Project, which tracks hate groups. “If you want to protest racists and anti-Semites, it needs to be peacefully and hopefully somewhere away from where those guys are rallying.”

The closest thing antifa may have to a guiding principle is that ideologies it identifies as fascistic or based on a belief in genetic inferiority cannot be reasoned with and must be physically resisted. Its adherents express disdain for mainstream liberal politics and prefer “direct actions.”

“When you look at this grave and dangerous threat — and the violence it has already caused — is it more dangerous to do nothing and tolerate it or should we confront it?” Sabaté said. “Their existence itself is violent … so I don’t think using force or violence to oppose them is unethical.”

One of antifa’s chief functions, members said, is to monitor right-wing and white supremacist websites like the Daily Stormer and to expose the extremist groups in dispatches on their own websites like ItsGoingDown.org. According to James Anderson, who helps run ItsGoingDown, interest in the site has spiked since the events in Charlottesville, with more than 4,000 followers added for a total of more than 23,000.

But antifa is “not some new sexy thing,” Anderson added. He noted that some who had scuffled with those on the right at Trump’s inauguration or at more recent events in New Orleans and Portland, Ore., were veterans of actions at the Republican National Convention in St. Paul in 2008, where hundreds of people were arrested, and at Occupy camps across the country.

Nonetheless, Anderson said, the far right’s resurgence under Trump has created a fresh sense of urgency. “Suddenly,” he said, “people are coming into your town with hate. It has to be confronted.”

One of the most vivid examples of antifa violence was in January at Trump’s inauguration, where a member of the movement punched prominent white supremacist Richard Spencer (who was pepper-sprayed by an antifa activist in Charlottesville). That blow started a national debate over whether it was morally justifiable to “punch a Nazi.”

Spencer drew distinctions among factions within the left-wing community. “It’s important to differentiate antifa from liberals,” he said. “I don’t think it’s an overstatement to say that antifa believes in whatever means necessary. They have a sadistic streak.”

Antifa activists have engaged with people who were less than outright neo-Nazis, raising questions about whether there is such a thing as legitimate political violence.

Some antifa members insist that they are merely reacting to aggression. “The essence of their message is violence,” Jed Holtz, an antifa organizer in New York, said of his right-wing foes. “The other side” — his side — “is just responding.”