路见不平，拔刀相助。
Come across injustice and draw one's sword to help the bullied; take up the cudgels for the injured party; give a helping hand to redress an injustice where it occures.
e.g. 他一生性情脾气不好，总是路见不平，拔刀相助。
He was bad-tepered all his life and would always take up the cudgels for others.
