BERKELEY, Calif.  — Berkeley, known as the home of the American free speech movement, was under heavy police watch on Thursday in advance of what was expected to be a large protest over a canceled appearance by conservative commentator Ann Coulter.

The author 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.

Coulter supporters said the university was attempting to silence their views.

Dozens of police wearing flak jackets and carrying 40 mm launchers that shoot “foam batons” flanked the university’s main plaza while a small group of protesters condemning Coulter staged one of two earlier rallies outside campus. Officers also took selfies with students in an attempt to lighten the mood.

Police erected barricades and refused to let participants enter the campus.

Protesters from the International Socialist Organization held what they called n “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.