The term 'Diamond Quartet, Briefly' is a crossword solution which refers to the four umpires who officiate a Major League Baseball game. UMP is an acronym for umpire, and the four letters in the solution refer to the four umpires who make up the Diamond Quartet. The Diamond Quartet consists of the home plate umpire, the first base umpire, the second base umpire, and the third base umpire. These four umpires are responsible for making calls on the field during a baseball game.