Erma Bergmann was one of three children born to Otto and Sophie Bergmann. Her father was a packinghouse butcher, while her mother, a ragtime pianist, wanted her only daughter to take piano lessons. However, Erma declined, preferring to play sandlot ball on the empty lot on the 1800 block of South Broadway, in the Soulard neighborhood of St. Louis with her two brothers and other neighborhood kids.
At 14 years old, Bergmann began playing third base in the St. Louis Amateur Softball League since other opportunities at school were limited. At 15, she played shortstop for the Melbas, a girls’ softball team at St. Louis Park, and pitched for the Phantoms, a boy's baseball team, recording 10 straight victories. She became a teenage standout and her talent drew notice from the scouts of the All-American Girls Professional Baseball League.
In an interview in 1992, Bergmann said her mother and some of her local teammates tried to talk her out of joining the league, saying that she would lose her amateur standing. She told her mother that she would try it and if she didn’t like it that she would come home. Instead, she played for six seasons on four teams.