Softball is a variant of baseball played with a larger ball (11 to 12 in. circumference) on a smaller field. It was invented in 1887 in Chicago, Illinois, United States as an indoor game. The game moves at a faster pace than traditional baseball. There is less time for the base runner to get to first while the opponent fields the ball; yet, the fielder has less time to field the ball while the opponent is running down to first base. The name softball was given to the game in 1926, because the ball used to be soft. A tournament held in 1933 at the Chicago World's Fair spurred interest in the game. The Amateur Softball Association (ASA) of America (founded 1933) governs the game in the United States and sponsors annual sectional and World Series championships. The World Baseball Softball Confederation (WBSC) regulates rules of play in more than 110 countries, including the United States and Canada; before the WBSC was formed in 2013, the International Softball Federation filled this role. Women's fast pitch softball became a Summer Olympic sport in 1996, but it and baseball were dropped from the 2012 Games; they will be reinstated for the 2020 Games. There are three types of softball. In the most common type, slow-pitch softball, the ball, which can measure either 11 or 12 inches in circumference depending on gender and league, must arch on its path to the batter, and there are 10 players on the field at once. In fastpitch softball, the pitch is fast, there are nine players on the field at one time, and bunting and stealing bases are permitted. Modified softball restricts the "windmill" wind-up usually used by fastpitch pitchers, although the pitcher is allowed to throw as hard as possible with the restricted back swing. Softball rules vary somewhat from those of baseball. Two major differences are that the ball must be pitched underhand—from 46 ft (14 m) for men or 43 ft (13.1 m) for women as compared with 60.5 ft (18.4 m) in baseball—and that seven innings instead of nine constitute a regulation game.Despite the name, the ball used in softball is not soft. It is about 12 in (about 30 cm) in circumference (11 or 12 in for slow-pitch), which is 3 in (8 cm) larger than a baseball. Softball recreational leagues for children use 11-inch balls until they participate in travel ball around age 12 and adjust to a 12-inch sized ball. The infield in softball is smaller than on an adult or high school baseball diamond but identical to that used by Little League Baseball; each base is 60 ft (18 m) from the next, as opposed to baseball's 90 ft (27 m). In fast pitch softball the entire infield is dirt, whereas the infield in baseball is grass except at the bases and on the pitcher's mound which are dirt. Softball mounds are also flat, while baseball mounds are a small hill. Softballs are pitched underhand, but baseballs are pitched overhand. This changes the arc of the ball when approaching the plate. For example, depending if the pitcher pitches a fastball, in softball the ball would most likely rise while in baseball because the pitcher is on a hill, the ball would drop.