To the Greasers, "rumble" means a physical fight between them and the Socs. For Ponyboy, it is a terrifying experience that he wants to avoid. For Darry, it is a way to defend their territory and show the Socs that they are not weak. For Johnny, it is a way to stand up for himself and his friends.
Having a "rumble" is not going to solve the problems between the Greasers and Socs. It will only escalate the violence and deepen the divide between the two groups. The root of the problem is not the physical conflict, but the social and economic inequalities that exist between them. Only by addressing these issues can they hope to find a lasting solution to their problems.