Few other features in sports history draw more wrath from opponents and more joy for the home team than Fenway Park’s left field wall. Dubbed The Green Monster because of its massive height and green paint, the wall in left field sends fly balls that would be home runs in other parks careening back into play, often at odd angles and high bounces. Originally known simply as The Wall, The Green Monster was painted green in 1947. The monster designation did not come until much later, but fans within the last several decades have grown fond of the left field wall. The wall birthed the Red Sox mascot that is, unsurprisingly, a green monster named Wally.

The Green Monster stands thirty seven feet, two inches (11.3m) high and was originally constructed of wood. It has since been covered with concrete and plastic and features a manual scoreboard at its base. Before it was painted green, The Green Monster was covered with advertisements. It featured a net at the top for several years to keep home run balls from hitting businesses on an adjacent street, but the net was removed from The Green Monster before the 2003 season and replaced with seating on top of the wall. The Green Monster seats have become extremely popular among Red Sox fans visiting the park.

The Green Monster wreaks havoc among outfielders unfamiliar with methods for playing the caroms off the wall. Because the wall is so high, it keeps high line drives from leaving the ball park for a home run, instead sending the ball ricocheting back into the outfield. Many outfielders misplay the ball off the wall, leading to an inordinate amount of extra-base hits, especially doubles. Seasoned outfielders – particularly Red Sox outfielders – have mastered the art of playing the ball off the wall and throwing out runners at second base.

The Green Monster is, however, susceptible to giving up short, high fly balls as home runs. Despite the wall’s height, its distance from home plate is relatively short at just over 300 feet (around 94 m), thereby allowing high fly balls to clear its top. Hadlock Field in Portland, Maine, home to Red Sox Double-A Minor League affiliate Portland Sea Dogs, houses a replica of The Green Monster, known locally as The Maine Monster. This allows minor leaguers on their way to the pros to practice taking caroms off the wall.