You didn't specify which chapter in your question so I have gone for Chapter Five of this great novel, which shows Cassie's confrontation with the Simms family after she accidentally bumps into Lillian Jean Simms. Mr. Simms is a white man who has land close to the Logans. Jeremy, his son, likes to walk to school with the Logans even though his father would not allow it if he knew about it. It is clear however from his actions in this chapter that he is very racist and believes that whites are superior to blacks in ever way. He demands that Cassie apologises to his daughter, callling her "Miss Lillian Jean," ad supports his daughter when she tells Cassie to get off the sidewalk and walk on the road itself. Note how Cassie describes him:
Then Mr. Simms jumped into the street. I moved away from him, trying to get up. He was a mean-looking man, red in the face and bearded. I was afraid he was going to hit me before I could get to my feet, but he didn't.
Mr. Simms is therefore a character that forces Cassie to realise the discrimination that exists in the world and how unfair life is. He manages to turn what was an event Cassie was looking forward to, travelling to market with her grandmother, into an immensely sad and tragic event as Cassie is forced to confront the rampant inequality that exists in the world.