Softball was invented around the beginning of the 20th century by American professional baseball players who wanted to keep in practice during the off-season late fall and winter months; the substitute game was played indoors.
Toward the end of the second decade of the century, Canadian amateur players began to play the new game outdoors, on playgrounds or other suitable fields; the game then rapidly became popular in Canada and obtained a foothold in the United States.
Extensive interest in softball began in the United States about 1930. The first national amateur softball tournament took place in Chicago, Illinois, in 1933 in connection with the world's fair then being held in that city. After about 20 years, when fast pitching began to dominate the game, slow-pitch softball was developed in order to give batters a better chance at hitting the ball. The popularity of slow-pitch softball spread abroad, especially in Mexico, Cuba, Japan, and Australia.
Also in 1933 the Amateur Softball Association (ASA) was founded to standardise the rules and govern the sport; it is still the governing body for softball in the United States.
Under the ASA annual sectional tournaments for both fast-pitch and slow-pitch softball are held for men and women. The winners of these tournaments and the championship team of the previous year meet in national championship tournaments. The first world softball championship was played in 1966.
Softball has become increasingly popular among women, particularly at the youth and collegiate levels. More than 600 National Collegiate Athletic Association (NCAA) member institutions sponsor women's softball teams, and national championship tournaments for women are held for three collegiate divisions. In 1991 women's fast-pitch softball was selected to debut as an event at the Olympic Games in Atlanta, Georgia, in1996.