Royals pitcher Amir Garrett lost his cool during a game Tuesday night -- throwing his drink on a fan who he says had been heckling him.
The shocking incident happened at some point during K.C.'s 9-2 loss to the White Sox at Guaranteed Rate Field in Chicago ... when Garrett had clearly heard enough from a fan who he claims chirped him on his way into the dugout.
Video shows as Garrett was heading down the steps to take a seat on his team's bench -- he stopped to engage in an argument with a man in a gray T-shirt.