We know we're looking at an allusion to the famous gunfight at the O.K. Corral. We don't know why, and we're too weary to puzzle out whether these three represent the Law (Wyatt and Billy Earp and whoever) or the Outlaws (the Clanton Boys and them).
What difference could it possibly make?
They're standing up for the interests of Smoke Wagon BBQ, which means they're standing up to be knocked down, whichever side they're on.
They stride through the dusty street, menace hooding their eyes. They tote their guns. By God, they will be put down.