As supporters of Donald Trump clashed violently with protesters demanding the release of Trump’s federal tax returns at a protest in Berkeley, California, on Saturday, shocking video of a Trump supporter delivering a full-force, unprovoked “sucker punch” to the face of a young woman emerged and quickly went viral on social media sites.

A reported 21 people were arrested at the Berkeley protest, and 11 more suffered injuries during the frightening brawl pitting what San Francisco’s KRON TV News described as “hundreds” of protesters on both the anti-Trump and pro-Trump sides. The protest was one of approximately 200 held nationwide on Saturday, April 15 — traditionally the deadline for submitting income tax returns.

The day was selected by protesters to highlight the fact that Trump has never released his tax returns, as has been customary for presidential candidates and presidents for the past 40 years. Trump is the first presidential nominee of a major party who refused to release his tax returns since 1976.

Though the pro-Trump demonstrators called themselves “free speech” advocates, witnesses said the group was comprised largely of extreme right-wing neo-Nazi and other white supremacist groups.

The Trump supporters in Berkeley today are NOT “free speech advocates”. They are white supremacist nazi terrorists, based on their actions pic.twitter.com/i5dp7RZqB3 — Tariq Nasheed (@tariqnasheed) April 15, 2017

Watch video of the protest at Berkeley below. The following video contains violent images and may be disturbing. Note that the incident in which a man with short, blonde hair and a blue shirt punches a woman in the face occurs at approximately the 30 second mark.

The horrifying moment was isolated and posted to social media by numerous users, who identified the attacker as 31-year-old Nathan Damigo, an Iraq War veteran, ex-convict, and leader of a white supremacist organization known as “Identity Evropa.”

The Trump supporting coward who punched a woman in Berkeley today is an Alt-Right, white supremacist named Nathan Damigo #TrumpsAmerica pic.twitter.com/fY9fJMHcsc — Tariq Nasheed (@tariqnasheed) April 16, 2017

According to The Southern Poverty Law Center, which monitors and reports on American hate groups, Damigo — a former corporal in the U.S. Marine Corp — founded Identity Evropa in March of 2016, two years after his release from prison. He served a five-year term after an armed robbery of a taxi driver.

Damigo was reportedly drunk at the time and pulled a gun on the taxi driver, believing the man to be Iraqi. According to a report in the Los Angeles Times, Damigo — a native of San Jose, California — suffered from “severe post-traumatic stress disorder, drug and alcohol abuse, paranoia and flashbacks,” and had attempted suicide following his first tour of duty in Iraq. But after a friend prevented him from carrying out the attempt, he returned to Iraq for a second tour.

While in prison, Damigo reportedly adopted racist, white supremacist beliefs after immersing himself in the writings of former Ku Klux Klan leader David Duke, as well as those of other extreme right-wing, racist writers.

Girl Puncher at Berkeley possibly identified as NATHAN DAMIGO, pal of Richard Spencer. pic.twitter.com/JLnniFLRoz — RogelioGarcia Lawyer (@LawyerRogelio) April 16, 2017

Damigo, however, says that he does not accept the term “racist” to describe his beliefs, preferring “identitarian.”

Whether Damigo will suffer legal consequences if indeed he is confirmed to be the man in the above video punching a young woman in the face remains unclear.

Berkeley police later posted pictures of weaponry and other prohibited items they had confiscated, mainly from the Trump supporters, at the Saturday protest.

Officers arrested 20 people and confiscated numerous weapons at #berkeleyprotests. Investigations continue. https://t.co/NYzodXdWsP pic.twitter.com/5YkWF5Clsk — Berkeley Police (@berkeleypolice) April 16, 2017

In addition to Damigo, the Berkeley protest reportedly attracted numerous prominent “alt-right” figures, including 41-year-old Kyle Chapman who is better known by his alias “Based Stickman,” referring to his practice of carrying a wooden stick — such as those seen above — as a weapon at public protests.

[Featured Image by Elijah Nouvelage/Getty Images]