Red Sox fans are going to HATE this ...
A group of L.A. Dodgers supporters secured a billboard right next to Fenway Park this week ... trolling the hell out of Boston for trading away superstar outfielder Mookie Betts last season!!
The savage sign was put up just yards away from The Green Monster ... located on the top of a building on Brookline Avenue.
The text? "Dear Boston, THANK YOU FOR MOOKIE BETTS. Sincerely, Dodgers fans and @Pantone294."
Of course, Boston jettisoned Mookie to LA just before the 2020 season began .