Fenway Park's Green Monster section of the At Bat - Ball manual scoreboard. The Green Monster is a popular nickname for the thirty-seven foot, two-inch high left field wall at Fenway Park, home to the Boston Red Sox baseball team. It is still updated by hand from behind the wall throughout the game. enway Park has been the home of the Boston Red Sox Major League Baseball team since it opened in 1912 and it is the oldest ballpark in MLB.