In some ways, they all fight for the same reasons -- because they are expected to. Their peers expect them to and so they must. But here are some differences:
- Dally -- because he is just a really violent person and very angry at the world.
- Darry -- because he likes anything that is a physical contest
- Johnny -- so he can belong to the gang and get away from home
- Soda and Steve -- because they are just sort of into the action and the excitement. Ponyboy says Steve fights for hatred, but I don't see it.
- Ponyboy says the only good reason to fight is self-defense.
Being a member of a gang is perfectly normal for Ponyboy and the boys in The Outsiders. It's also clear from Ponyboy's descriptions in chapter one that the boys are classified according to whether they are Socs—"the jet set, the West-side rich kids"—or "greasers, all us boys on the East Side."
The Socs get into fights for no reason other than "for kicks." The greasers, of which Ponyboy is one, "have a gang fight once in a while." Each gang member has his own reasons for fighting, but Ponyboy points out that they never set out to hurt anyone. For them, it's more about protecting their image and looking out for each other.
During one misunderstanding, Johnny kills a Soc in self-defense, and he and Ponyboy need to take cover somewhere far away so as not to be discovered. Dally helps them get out of town; meanwhile, the Socs and greasers "are having all-out warfare all over the city" (chapter five) because of the incident. The two boys stay away, and during their hideout they become unlikely heroes, saving some children from a burning building. As the newspaper headline reads: "JUVENILE DELINQUENTS TURN HEROES" (chapter seven). However, the cost of their actions is high, as Johnny is seriously hurt and later dies from his injuries.
It is this incident that sparks an arranged fight between the Socs and the greasers, and regardless of their motivations, all the greasers want to participate in this "rumble" because they feel the Socs are to blame for everything that has happened. As Ponyboy says, "Greasers may not have much, but they have a rep."
As the boys prepare for the rumble, Soda admits that he likes the fact that fights are like contests. Steve just likes to "stomp the other guy good," and Darry likes to show off his muscles because it is a show of strength. Two-bit thinks fights are the thing to do, but Ponyboy admits that he does not like fighting. He sums it all up when he says (in chapter nine),
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.