Before the big rumble between the Socs and Greasers, Ponyboy briefly mentions that there is a 'no weapons' rule during the gang fight. This meant that neither gang is allowed to use anything that could be used as a weapon, which includes "bicycle chains, blades, pop bottles, pieces of pipe, pool sticks, and heaters." Pony also mentions that some of Shepard's gang is used to fighting with weapons because they are criminals with no future. Unlike Shepard's gang, the Greasers never use weapons during gang fights. However, Ponyboy does mention that they occasionally use knives because they are always carrying them. He says that none of the Greasers are truly interested in seriously hurting anybody, including Johnny, who accidentally killed Bob Sheldon.
In addition to not using weapons, the number of participants needs to be roughly the same on both sides. While the Greasers are short-handed, they enlist help from the Brumly boys and Shepard's gang to even their numbers.
The rumble also begins when someone throws the first punch. In the novel, Paul Holden throws the first punch and hits Darry in the face. The rumble ensues after Paul hits Darry, and the Greasers end up defeating the Socs.
In most gang fights, there were no rules. Knives, chains, bottles, pipes, pool sticks and "sometimes even heaters" were used, especially by Tim Shepherd's gang. But in this particular rumble with the Socs, there would be no weapons, only "skin" (fists). This was confirmed by Cherry when Ponyboy went to confer with her.
"They play your way. No weapons, fair deal. Your rules."
Each side chose a man to start the fight and throw the first punches. Because Darry was the biggest and strongest, he volunteered for the greasers.
"I'll take on anyone."
An old high school friend, Paul Holden, agreed to represent the Socs. The two stalked each other for a few moments, circling until Holden threw a hard right hand "that would have felled anyone by Darry." Weapons actually were used--one of the Brumly boys used a pipe, and the leader of that gang was "working over one of his own men" for doing so.