The Breaker (2007)

Yi "Shioon" Shi-Woon's daily life at Nine Dragons High School consists of beatings by fellow student Ho Chang and his gang. But one day, a mysterious man named Han Chun Woo witnesses one of these beatings and instead of helping him, claims Shioon as a coward for refusing to fight back, which even adds more insult to injury. Much to Shioon's surprise, he discovers that Chun Woo is actually the new substitute English teacher at his school.