The A League Of Their Own true story is about the All-American Girls Professional Baseball League, a real league from 1943 to 1954. The Penny Marshall film loosely follows the story of the AAGPBL, which was formed in 1943 during World War II when Major League Baseball was in danger since men were being drafted for war. In the same way women stepped up to work men's factory jobs, they did the same for baseball. The film focuses on sisters Dottie Hinson (Geena Davis) and Kit Keller (Lori Petty), who are recruited for the Rockford Peaches.
https://screenrant.com/league-their-own-movie-true-story-history/