Why did cherry hit pony boy?

Cherry Valance hit Ponyboy in "The Outsiders" because she was upset and frustrated after a confrontation with her boyfriend, Bob, who had just attacked Ponyboy and Johnny. She was trying to express her emotions and the complexity of her feelings about the violence between the Socs and the Greasers. Cherry's action signifies the tension between their worlds and her internal conflict regarding her relationships and social status.