Life in Chicago sure is busy for Rosie. Between school and working as an usher in her father's nickelodeon, she has little time for play. She hears all about the Chicago baseball scene, though, from Abe, one of her younger brothers. He's always talking about the fierce rivalry between two teams, the Tigers and the Chavarim. Things really heat up when the Chavarim's top player gets hurt, with only one deciding game left in the season. The team's in a bind and they need help...fast!

With an arm and a spirit stronger than most boys', Rosie seems to her brothers an obvious choice for a substitute player. Maintaining her disguise as a boy to play with the all-male Chavarim is a big enough challenge without having to deal with bullies on the other team -- and the sidelines -- who are standing between her and a win. But fortunately for the Chavarim, nothing can stop this girl!