It's a one word title: Jumped. It's simple and concise, and it doesn't give us any clue that the book is nuanced and complex and about oh so much more than one girl jumping another girl after school.
After the first three chapters of the book, we think we know the story: perceived insult, school day, attack. Badda bing bang boom. But as we read, we start to understand that the characters are slightly more (but not much more) than their archetypes.
Dominique is more than a girl with a temper, Leticia maybe does have a conscience, and Trina might be more than her bubbly superficial personality. This is when we realize that this story about a fight is actually about so much more. It's about the school where the altercation takes place, the authority figures and what power they actually have, as well as how the students function within the school. And especially the decisions and indecision that leads to the attack.
But the title is still short. As Williams-Garcia has said, these attacks just happen, and they usually happen in a short amount of time. So even though the book is multifaceted, it boils down to a senseless beating that changes only Trina, not the attacker or the witness.