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 USA 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 — one for obstructing an officer and wearing a mask to evade police, and another for possessing a knife.

Coulter previously said she was forced to cancel a speaking event at the University of California, Berkeley, although she added that she might still “swing by to say hello” to her supporters, prompting police and university officials to brace for possible trouble. She was not spotted at the rallies.

Several hundred people gathered for an afternoon rally supporting Coulter in downtown Berkeley.

“It’s a shame that someone can’t speak in the home of the free speech movement,” said Wilson Grafstrom, an 18-year-old high school student from Menlo Park.

He wore a military grade helmet with a “Make America Great Again” sticker across 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 main Sproul Plaza also wore military grade helmets and body armor.