I had it then. Soda fought for fun, Steve for hatred, Darry for pride, and Two-Bit for conformity. Why do I fight? I thought, and couldn't think of any real good reason. There isn't any real good reason for fighting except self-defense.
This quote said by Ponyboy reflects his thought on the nature of aggression and fighting in general. He tries to figure out for himself the reasons he fights for and he uses the examples of his friends and family to understand what makes them fight to deduce his own. Sodapop or Soda for short is his younger brother, who is still a kid, so it is completely understandable that he sees fight as another kind of game. Steve is embittered enough to experience intense aggression and frustration.
This makes him see the fight as the way to vent his anger and get rid of it. Darry Curtis, Ponyboy’s older brother and the leader of the gang, sees fights as the way to maintain his status and hierarchy and to prove that his gang is still strong and can protect itself from the rivals. Two-Bit fights just because everyone else does so, so he wants to just be a part of the group.
Ponyboy denies that reasons one after another, now he is sure why he is NOT fighting. But he can’t look at himself critically enough. He sees the issues of the others that make them fight and clearly understands the reasons they do it - but for himself Ponyboy can’t imagine any other reason to fight except the most natural: self-defence. The paradox is that the member of the gang that is literally fights for survival behaves as a normal kid. He is so well-protected by his brother from the hazards of the outer world that he maintains a healthy attitude to fighting, considering it not a way to solve the problems, but the thing he can resort to only if his life or health is endangered.