Read "Call Him Nemesis" by Donald E. Westlake online for free on Textopian. Full text with search, annotations, highlights, and AI-powered reading aids.
Hallowe'en is a good time for a rumble. There's too many kids around for the cops to keep track of all of them, and if you're picked up carrying a knife or a length of tire chain or something, why, you're on your way to a Hallowe'en party and you're in costume. You're going as a JD.
The problem was this schoolyard. It was a block wide, with entrances on two streets. The street on the north was Challenger territory, and the street on the south was Scarlet Raider territory, and both sides claimed the schoolyard. There had been a few skirmishes, a few guys from both gangs had been jumped and knocked around a little, but that had been all. Finally, the War Lords from the two gangs had met, and determined that the matter could only be settled in a war.