The context of the following conversation is After taking karate lessons, Austin taught the bully a lesson by punching in the face.:
Austin says I got back at that bully today. Those karate lessons paid off. I punched him right in the face when he started teasing me..
The friend responds Did he hit you first?.
Austin responds Well , no but he is always  bothering me . He needed to be taught a lesson..
The friend responds You should only hit someone if he  hits you first. But I'm glad you actually fought back for once instead of running away..