Why is Cherry going to say Johnny acted in self-defense?

Cherry is likely to say that Johnny acted in self-defense because he was protecting himself from being attacked by the Socs, who were known for their violent behavior. She understands that Johnny felt threatened and had no choice but to defend himself against a group that was intent on harming him. Cherry recognizes the context of the situation and wants to highlight Johnny's fear and the dire circumstances he faced, which led to his actions.