SAN FRANCISCO — The University of California Police Department on Friday arrested a suspect in the assault of a conservative activist on the Berkeley campus, reviving a debate over free speech at colleges.

Neither the suspect, Zachary Greenberg, nor the man he is accused of punching, Hayden Williams, a field representative of the Leadership Institute, an organization that provides training to conservative campus groups, was a student at the university.

The attack on Feb. 19 took place at Sproul Plaza, the birthplace and symbol of the Free Speech movement, the protests by students in the 1960s demanding greater political expression. Mr. Williams was helping a campus group that was recruiting members.

Conservative groups said the assault on Mr. Williams served as a symbol of what they say is continued intolerance toward conservative views on college campuses. Mr. Williams appeared on Fox News programs with a black eye, and videos of his assault were widely shared on social media.