The action takes place at school during gym class. Kids are playing volleyball. And one of the girls accidentally hit a boy on the head with a ball. She walks up to him to say sorry. Bella: "I'm sorry I told them not to let me play." Boy: "You're Isabella, right?" Here comes up another girl and say: "She's got a great spike, huh?" Could you tell me what she means by "great spike"? Thanks!