SAN JOSE (CBS SF) — A few hundred protesters fought with supporters of Donald Trump after the presidential candidate’s rally in San Jose Thursday night.

Over a dozen fights broke out in the crowd.

Punches were thrown, violence erupted. Even police had to retreat.

• EARLIER: Trump Jumps Fence To Speak At California GOP Convention

The San Jose Police Department made a number of arrests after the Trump Rally and said an officer was assaulted.

Protesters followed Trump supporters to their cars as they left the convention center. Around the corner and away from police protection on San Carlos Street, a mob mentality took over.

A young man wearing a “Build The Wall” T-shirt was assaulted by several young men. Fearing for the man’s safety, KPIX 5 reporter Len Ramirez yelled at him to get away.

For several minutes, there was no police presence and protesters thumped Trump supporters’ cars in the parking garage as they tried to leave.

• ALSO READ: San Jose Mayor Slams Trump Over Post-Rally Violence

Outside again, there was another assault, and another. Street fights broke out on Almaden Avenue.

Andrew Acevedo, of Redwood City, said he was assaulted several times while getting stuck inside the anti-Trump protest rally.

As police tried to restore order protesters forced a police pickup to retreat.

Police lines formed again, but the crowds only grew.

Another young man was chased down like prey. He ran until finding some police officers who stopped his attackers.

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Some protesters grabbed Trump hats and tried to burn them, while others banged on the cars of supporters trying to leave the rally.

Police declared the gathering an unlawful assembly about 30 minutes after the rally ended.

Trump spoke for about 50 minutes to the crowd of thousands at the rally, harping on Democratic candidate Hillary Clinton and calling her foreign policy speech earlier in the day “pathetic” and “sad to watch.”

On Friday morning, the presumptive Republican nominee tweeted about the protest.

Rally last night in San Jose was great. Tremendous love and enthusiasm in the hall. Big crowd. Outside, small group of thugs burned Am flag! — Donald J. Trump (@realDonaldTrump) June 3, 2016

John Podesta, chairman of Hillary Clinton’s campaign, condemned the violence.

Violence against supporters of any candidate has no place in this election.

https://t.co/PY4vYYszVf — John Podesta (@johnpodesta) June 3, 2016

Trump is expected to appear in Redding, about 150 miles north of San Francisco, for a rally on Friday.