What did Sergio remember about a time when his cousin Ralph was grabbed by the police and frisked?

Sergio gets on the train with Gideon. They do not sit together. The lights go out and the train slows and stops. They all wait for the power to go back on. A white man gets frustrated and says that he has to get to work. He gets up and starts to try to go out the door. The train starts again. The man falls and hits his head.