Unrest on the UC Berkeley campus Wednesday resulted in $100,000 in damage and just one arrest, officials said.

The university Thursday defended the hands-off approach of its police force in the midst of the chaos that broke out after a group of 150 or so black-clad, masked people hijacked a previously peaceful protest against a far-right provocateur, Milo Yiannopoulos, who had been scheduled to speak at UC Berkeley’s student center Wednesday night. The protest forced officials to cancel Yiannopoulos’ appearance.

Six minor injuries were reported in the fray, said Dan Mogulof, a spokesman for the university, and the one arrest was for failure to disperse.

In the city of Berkeley south of the campus, where protesters later paraded through the streets, some smashing store windows — about 15 in all — and spraying graffiti, there were no arrests, said Officer Byron White, a spokesman for the Berkeley Police Department.

White added that officers, even with extra staffing planned for the evening, were kept busy shutting off roads from protesters darting through traffic, saying that the department’s main priority was “the protection of life,” even if that meant some vandalism. No major injuries were reported, White noted.

Mogulof said that while dozens of officers were called in throughout the University of California system, the “paramilitary force that showed up with weapons” was an “unprecedented event” that upended security plans.

“We know we’re always going to be second-guessed, and there’s always going to be Monday-morning quarterbacking about what happened,” Mogulof said.

President Trump weighed in on Twitter, tweeting: “If U.C. Berkeley does not allow free speech and practices violence on innocent people with a different point of view - NO FEDERAL FUNDS?”

The masked vandals, most, if not all, said to be from outside the campus, shut down Yiannopoulos’ talk before it started.

Wearing “ungovernable” logos adorned on all-black jumpsuits, with bandannas and masks covering their faces, the self-described anarchists struck with near-military precision.

They crept out of the crowd as dusk set in outside the three rows of zip-tied fencing that police set up, trying to prevent a repeat of the scene at UC Davis, when Yiannopoulos was prevented from speaking in January. In ones and twos, and then all at once, the vandals ripped the fencing down, daring the dozens of police behind the barrier to do something about it.

As Yiannopoulos waited inside the Martin Luther King Jr. Student Union, still more than two hours before he was supposed to take the stage, the police fell back inside the building under fire from Molotov cocktails, bricks and a host of other makeshift weapons.

“Very often when police have waded into large crowds, the situation can get out of control very quickly,” Mogulof said of why police didn’t confront protesters, adding that the risk was too high of many innocent protesters getting injured if police were to use force.

All the while, the vast majority of the crowd was peaceful, many of them students, wearing jeans and hoodies, not the “paramilitary” gear, clutching cardboard signs bashing Yiannopoulos, of the far-right publication Breitbart News, as hateful, as dangerous, as cruel. Many of the onlookers had never seen anything of the sort in Berkeley before, where protests are plentiful, but generally peaceful.

As police watched from skirmish lines on the other side of the student center’s glass, the hooded figures wreaked their work, throwing pieces of discarded metal fencing through the glass windows and shooting flares at the building.

Many of those flares and fireworks narrowly missed other protesters who were dancing peacefully in the middle of the chaos, bopping their heads to a booming speaker system that someone brought into the plaza.

After a spell, officers emerged on the second-floor balcony, saying over a loudspeaker that Yiannopoulos was gone, repeatedly threatening to use force that never came.

In speeches on other campuses, Yiannopoulos has publicly outed trans students, and he has ridiculed the Black Lives Matter movement and a host of other left-leaning organizations.

Mogulof said the department had multiple investigations ongoing, saying police were “not done with these incidents yet,” adding that “we believe deeply there should be consequences for violations of the law.”

Michael Bodley is a San Francisco Chronicle staff writer. Email: mbodley@sfchronicle.com. Twitter: @michael_bodley