The Yankees and Mets almost fought each other in the middle of the diamond Sunday night ... and it was all 'cause a pitcher in the Pinstripes' dugout had been whistling.
For real.
The wild scene all went down at Citi Field ... just seconds after Giancarlo Stanton hit a huge home run in the 7th inning of the final game of the New York teams' weekend series.
As Stanton was rounding the bases, Francisco Lindor yelled at the Yanks superstar ... while making a whistling motion.