Unlike his brothers, Ponyboy does not like to fight. Soda likes it for the "action. It's a contest." Darry likes fighting because he enjoys all tests of strength. Soda's pal, Steve, likes to fight, too. Pony wasn't afraid of fighting:
"I'll fight anyone anytime, but I don't like to."
But this rumble is different. As Dally told Pony and Johnny before the fire, the Socs had agreed to stay out of greaser territory if they lost the fight. For Pony, it meant a way to pay the Socs back for all the trouble they had instigated: For making Johnny kill Bob, for forcing Pony and Johnny to leave town, and for causing Johnny's injuries. The greasers were also short-handed, with Dally and Johnny in the hospital. But most of all, it was a way to show that the greasers--the boys from the wrong side of the tracks--were better than the privileged Socs at something.
Right then the most important thing in my life was helping us whip the Socs. Don't let him make me stay home now. I've got to be in it.