In baseball statistics, earned run average (ERA) is the mean of earned runs given up by a The all-time record for the lowest single season earned run average by a pitcher pitching or more innings is , set by Bob Gibson in. In baseball, earned run average (ERA) is a statistic used to evaluate pitchers, calculated as the The lowest single- season ERA in league history was posted by Tim Keefe, whose ERA in innings pitched for the National League's Key · National League · American League · Other major leagues. Baseball Almanac researches the all time earned run average leaders during a single season and lists the top one-hundred in baseball history. Active Career Leader: Clayton Kershaw, Earned Run Average ; All-Time Current Regular Season Leader: 2 players tied, Earned Run Average. Statistic Description: 9 * ER / IP For recent years, leaders need 1 IP per team game played. Bold indicates lowest ERA using current stats Gold means awarded. Single- Season ERA LeadersTim Keefe+//, micedesigning.com Leonard// , micedesigning.comai Brown+//, micedesigning.com Gibson+//, micedesigning.comy.