Earned Run Average (ERA) is a statistic used in baseball to measure a pitcher's effectiveness. It calculates the average number of earned runs a pitcher allows per nine innings pitched. An earned run is a run that scores without the benefit of an error or a passed ball, reflecting the pitcher's performance more accurately. To calculate ERA, the formula is: (Earned Runs × 9) ÷ Innings Pitched. A lower ERA indicates better performance, as it means the pitcher allows fewer runs. This statistic helps teams and fans evaluate a pitcher's ability to prevent scoring and contribute to their team's success.