"Our experience on the streets was that we were defended by people who came - as anti-fascists - to do that", said Sara Kurshner of the National Lawyers Guild. Civic Center Park where a "No to Marxism in America" rally was scheduled.
They also fired a rubber bullet at a demonstrator who tried to cross a barricade into Martin Luther King Park.
The move came as officials erected fencing at Alamo Square park and a large contingent of police monitored the location to prevent possible violence.
Gibson then went behind a line of police wearing riot gear.
Tensions ran high among a beefed up police presence and the appearance of counter protesters. If every event has the potential to become violent, fewer people are likely to gather. Gibson, who condemned white supremacism and neo-Nazism at a recent rally, says his group is not racist in nature. He blamed San Francisco Mayor Ed Lee and House Minority Leader Nancy Pelosi, whose district includes the city, for categorizing the group as white extremist and raising tensions. "You are not welcome at this event and please stay away".
Qatar hits out at Saudi's restrictions on Haj flights
The move sparked a backlash in Doha, where authorities said the pilgrimage had been used as political ammunition. Saudi Arabia recently reopened its land border to Qatari pilgrims and offered to fly them to hajj.
Counter-protests against right-wing rallies in San Francisco and Berkeley over the weekend remained largely peaceful until Sunday, when the mob of masked agitators stormed into Berkeley's Civic Center Park to disrupt a "No Marxism in Berkeley" event.
The city and the police department had prepared for protests by erecting a chain-link fence around the park, according to the San Francisco Chronicle, and had also set up barriers to keep protesters away from residential streets with a "one-block buffer zone".
Police said helmets and masks of any kind, including gas masks, are prohibited.
The skirmish broke out at the Berkeley protest between several dozen left-wing demonstrators and a handful of right-wing supporters.
Later in the day, protesters converged on Berkeley's Ohlone Park, where the protest eventually subsided and disbanded. By 4 p.m., most of the crowd had left the area, leaving only a homeless man sleeping in the park.