Overview
An earned run represents a run scored that the official scorer judges would have occurred without errors or passed balls by the defense. ERA is calculated as earned runs times nine divided by innings pitched, making earned runs foundational to pitcher evaluation. Runs scoring after a runner reaches base on an error are unearned, serving to separate pitching performance from defensive quality. However, earned run determination involves scorer discretion and requires hypothetical reconstruction of what would have happened without errors, making it imperfectly objective. To address this limitation, sabermetrics supplements ERA with FIP (Fielding Independent Pitching), which evaluates pitchers solely on strikeouts, walks, hit-by-pitches, and home runs.