Jonathan Brophy, an undergraduate psychology major, stood in the Student Activities Center Plaza gripping a hand-made sign against the wind. The sign illustrated a sea of blue guppies, eating a slightly smaller fish wearing a crown. Brophy held it high above his head while he chanted with the crowd, “Education is a right. Fight, fight, fight, fight!”

The Radical Student Union appears as a mysterious entity—showing up at certain events and not being listed on the university’s homepage. Members surface during events like protests, especially those...