What does “Illegal Pitch” mean?

Definition: A pitch delivered outside the rules (e.g., not meeting the required arc, stepping outside the pitching area, quick pitching). Rule/Context Note: In SPN/USA, an illegal pitch results in a ball on the batter and may allow runners to advance, depending on the rule variation. When It Matters: Umpire calls, pitch count, pitcher consistency. Interlinks: Pitching Arc • Balk • Strike Zone