What does 2 Samuel 20:21 mean?

There's a man named Sheba, son of Bichri, from the hill country of Ephraim. He's rebelled against King David. If you hand him over, I'll leave your city alone.' The woman said, 'His head will be thrown over the wall to you.' 2 Samuel 20:21 - Modern Text Bible

(Joab explains he's only after Sheba, the rebel leader. The woman promises to deliver Sheba to save her city.)