PONY Baseball and Softball originated in Washington, PA in 1951. The league’s goal was to help 13 and 14-year-old players transition from the smaller Little League baseball diamond to a regulation size diamond. The league grew rapidly through word of mouth, and by the end of the second season in 1952, PONY grew from the original six teams in Pennsylvania to 505 teams in 106 leagues around the United States. This growth allowed for a national tournament, culminating in the first Pony League World Series in the summer of that year.

PONY continued to grow over the next several years, adding new leagues for different age groups. In 1970, Fort Worth, TX developed the Mustang League using a diamond with 60-foot base paths and a 46-foot distance from the pitching mound to the plate, catering to the 9 and 10-year-old players.

The Mustang-9 World Series began in 2014 in Walnut, California at Creekside Park and has run there since. The tournament has hosted American teams from California, Hawaii, Texas, Illinois, Kentucky, North Carolina, Virginia, and New York, as well as international teams from Mexico, the Caribbean, the Philippines, the Dominican Republic, and Panama over the past five years.

California won the first four Mustang-9 World Series titles (2014-2017) with teams from Santa Clarita, Simi Valley, Emerald, and Los Alamitos. However, 2018 brought a World Series champion from a new state when Mililani, HI beat Mexico Zone champions Tijuana, Baja California 10-0 in the final game.

This year's tournament runs from July 19-22 at Keating Park in Vacaville, California and will again host teams from around the United States as well as international competitors.