tl;dr

The Harmonica Incident took place on a New York Yankees team bus on August 20, 1964, en route to O'Hare International Airport. Infielder Phil Linz, slightly resentful at not being played during a four-game sweep by the Chicago White Sox that was believed at the time to have seriously set back the Yankees' chances at that year's American League pennant, began playing a harmonica in the back of the bus.

Manager Yogi Berra, feeling that Linz's behavior was inappropriate given the team's recent poor performance, angrily called on him to stop, whereupon Linz threw the harmonica and loudly complained about being singled out despite not having been at fault for the losses.

If you've got time to kill and/or you must know more - the full article is ~7,500 words. I'm not a sports guy so I tapped out early. I would have been willing to read up to ~1,500 words though.