MLB star Jarren Duran was caught on a hot mic calling a heckler an anti-gay slur on Sunday ... and after receiving backlash for hours, the outfielder issued a mea culpa, apologizing for his "truly horrific" language.
The 27-year-old Red Sox player let the f-word fly when he stepped into the batter's box during the sixth inning of Boston's blowout loss to Houston.
You can hear in audio from the game's broadcast ... as a man in the Fenway Park stands chirped him about needing "a tennis racket" while at the dish -- he fired back by calling the guy a "f***ing f****t.