Crunch is roleplaying gamer slang for the actual game mechanics of a system or setting, probably in reference to number-crunching. It is the opposite of Fluff, which describes things in an in-universe sense. For example, a special ability or feat's fluff might say that "You grew up in a school for mages, and have thus learned some of the rudiments of magic"; the associated crunch could be a +2 bonus to Spellcraft and Use Magical Device checks.
One of the traditional failings of powergamers is a focus on crunch to the exclusion of the fluff, creating characters that are mechanically powerful but make little sense from an in-character perspective.
Examples of Crunch Overwhelming Fluff
- League of Legends and the handling of the lore, after Riot Games realized they could safely ignore it and the majority of the playerbase would not quit, or would rather watch esport athletes score skillshots than follow the lore. Riot decided to abandon the Institute of War and almost several years of story to focus on the esports scene. Cue butchery of characters on par with Matt Ward.