What is the initial incident in the Friday everything changed?

In "The Friday Everything Changed" by Anne Hart, the initial incident occurs when a group of schoolchildren, including the protagonist, is confronted by the realization that girls are not allowed to participate in a game of Baseball. This moment sparks a desire for equality and leads the girls to challenge the existing gender norms, ultimately changing their relationships and the dynamics in their classroom. The incident sets the stage for the broader themes of empowerment and social change that unfold throughout the story.