Earned run average

Earned run average (ERA) is the average number of earned runs a pitcher allows per nine innings pitched. It measures run prevention while excluding runs judged unearned because of fielding errors or passed balls.

Earned run: A run charged to a pitcher under baseball’s scoring rules, excluding runs caused by specified fielding errors or passed balls. Only earned runs enter the numerator of ERA.
Adjusted ERA+: A park- and league-adjusted pitching statistic that expresses a pitcher’s ERA relative to the league average, with 100 as average. ERA+ adjusts ERA for scoring conditions and makes comparisons across seasons more useful.
WHIP: A pitching statistic calculated as walks plus hits allowed per inning pitched. WHIP measures baserunners allowed rather than runs charged.
Dutch Leonard’s 0.96 ERA: The 0.96 earned run average posted by Dutch Leonard for the Boston Red Sox in 1914. This exceptionally low season ERA illustrates the statistic’s historical extremes.
Innings pitched: A measure of the outs a pitcher records, expressed in innings and thirds of an inning. ERA uses innings pitched as its denominator, scaled to nine innings.
Earned run average in Major League Baseball: The use and interpretation of ERA within Major League Baseball’s official statistics and historical records. Major League records provide the most familiar setting for ERA comparisons.
Expected ERA: A Statcast statistic estimating ERA from the quality of batted balls, strikeouts, and walks. Expected ERA tests whether actual ERA aligns with outcomes implied by contact quality.
Bob Gibson’s 1.12 ERA season: The 1.12 earned run average Bob Gibson recorded for the St. Louis Cardinals in 1968. Gibson’s season helped prompt a reduction in the major-league pitching mound.
Baseball scoring rules: The official rules and conventions used to record events and statistics in baseball. Scorers apply these rules to decide whether a run is earned.
Pitching triple crown: An honor for leading a league in wins, strikeouts, and earned run average in the same season. ERA is one of the three traditional measures in this pitching achievement.

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