From ESPN.com's action sports department, and specifically this article by Brian Kamenetzky: "a growing number of action sports athletes (call 'em ACAs for short) are finding their bliss on four wheels. "
Wait... action sports athletes... ACAs... in what twisted universe does that make sense? We could, perhaps, excuse it as a typo, albeit an unbelievably prominent typo - except that Kamenetzky then repeats the ACA acronym throughout the rest of the article. My guess is that he was trying for "Action Crossover Athletes", or "Action Sports Crossover Athletes" - but the recurring presence of an unintelligible acronym renders the article in its present form nothing more than a punchline.
Note to self: when creating a snazzy acronym, make sure that it, you know, makes sense. Screenshot here.