BERKELEY, Calif. — Berkeley, known as the home of the free speech movement, was under heavy police watch on Thursday as hundreds of people waving American flags and chanting gathered in a park to protest a canceled appearance by conservative commentator Ann Coulter.

University police erected barricades and refused to let any protesters enter the campus. Four people were arrested.

Police had prepared for possible violence between supporters and opponents of Coulter, but there were no major confrontations at the raucous rally, largely because members of an anti-fascist group did not show up in force.

University officials said they had been unable to find a suitable and safe spot for her to speak and offered a May 2 date.

Despite the cancellation, Coulter had said that she might “swing by to say hello” to supporters, prompting police and university officials to brace for possible trouble.

She was not spotted at the rallies but said Thursday on Fox News’ “Tucker Carlson Tonight” that she had planned a “searingly brilliant speech on immigration” enforcement.

Several hundred Coulter supporters gathered for an afternoon rally at Martin Luther King, Jr. Civic Center Park in downtown Berkeley. “It’s a shame that someone can’t speak in the home of the free speech movement,” said Wilson Grafstrom, 18, a high school student.

He wore a military grade helmet with a “Make America Great Again” sticker on the back, goggles, gas mask and knee pads. He blamed Coulter opponents for forcing him to gear up for problems.

Many at the park rally about a mile from the university’s Sproul Plaza also wore military-grade helmets and body armor.

The tension illustrates how liberal bastion Berkeley has emerged as a flashpoint for extreme forces amid the debate over free speech in a place where the 1960s U.S. free speech movement began.

Officers took selfies with students in an attempt to lighten the mood.

Protesters from the International Socialist Organization held what they called an “Alt Right Delete” rally with signs reading “Refuse Fascism” and “Fascist free campus.” The group endorses free speech, and some members oppose the way Coulter and others have co-opted the free speech movement.

“I don’t like Ann Coulter’s views, but I don’t think in this case the right move was to shut her down,” said graduate student Yevgeniy Melguy, 24, who held a sign that read, “Immigrants Are Welcome Here.”

Chancellor Nicholas Dirks sent a letter to the campus Wednesday saying the university is committed to defending free speech but also to protecting its students. “This is a university, not a battlefield,” Dirks said in the letter.