Last summer, Angus Cloud was walking through Manhattan with his friends when a woman approached him. “She asked me if I would be down to do an audition, but she didn’t exactly say what it was for. I thought it was some type of scam,” Cloud says in a phone interview. The woman worked for Jennifer Venditti, the casting agent responsible for populating films like American Honey and Good Time with people who don’t look like typical movie stars.

At the time, the Oakland, California native was working at a chicken-and-waffles restaurant...