Book Knight was tired, bruised, frustrated, and sick of Blueblood's attitude, so he punched the prince. Who knew how much praise you could get for assault on royalty?
Book Knight is a superhero who scares villains away from even thinking of committing a crime. Twilight is a princess who tries to reform said villains through friendship. Book thinks that she's weak, and Twilight think's he's too extreme. Oh dear.