Bases in the context of a "ballpark quartet" refers to the four points, usually made of bags or plates, on a baseball field that a player must touch in order to score a run. The bases are positioned in a diamond shape, and a player progresses from first base to second base, then third base, and finally to home plate.
Note: The provided meaning of the answer is for the latest New York Times crossword puzzle clue: Ballpark quartet. Explanations are generated by AI and may be inaccurate.