home run was made 250 feet. Until 1929 (AL) and 1931 (NL), a ball that bounced over the outfield fence in fair territory was a home run, not a double. After that, the rules remained virtually static for decades. In 1961, the 162-game schedule was adopted. In 1969, the pitcher's mound dropped five inches and the strike zone reduced: from the armpits to the top of the knees. In 1973, the American League adopted the designated hitter rule. This was probably the most controversial rule change in baseball's history and is still subject to lively debate. It was not adopted by the National League until 2022. Also controversial when adopted was the later introduction of interleague play. The most recent significant rule changes, banning the use of steroids and other performance-enhancing substances, have had widespread support as protecting the integrity of the game. The use of steroids by many players over the last two decades has called into question records for both hitting and pitching. Gameplay General structure Baseball is played between two teams with nine players in the field from the team that is not batting at that point (the batting team would have one batter in play at "home plate" on the field). On a baseball field, the game is under the authority of several umpires. There are usually four umpires in major league games; up to six (and as few as one) may officiate depending on the league and the importance of the game. There are three bases. Numbered counterclockwise, first, second, and third bases are cushions (sometimes informally referred to as bags) shaped as 15 in (38 cm) squares which are raised a short distance above the ground; together with home plate, the fourth "base", they form a square with sides of 90 ft (27.4 m) called the diamond. Home plate is a pentagonal rubber slab 17 in (43.2 cm) wide. The playing field is divided into three main sections: The infield, containing the four bases, is for general defensive purposes bounded by the foul lines and within the grass line (see figure). The outfield is the grassed area beyond the infield grass line between the foul lines and bounded by a wall or fence. Foul territory is the entire area outside the foul lines. The pitcher's mound is located in the center of the infield. It is an 18 ft (5.5 m) diameter mound of