The dean of Berkeley’s law school is known as a staunch supporter of free speech, but things became personal for him when pro-Palestinian students disrupted a celebratory dinner party for some 60 students at his home.

Erwin Chemerinsky, the law school dean, hosted the dinner on Tuesday night in the backyard of his Oakland, Calif., home. The party was supposed to be a community building event, open to all third-year law students, with no speeches or formal activities.

But a third-year law…