<P> In baseball, earned run average (ERA) is a statistic used to evaluate pitchers, calculated as the mean of earned runs given up by a pitcher per nine innings pitched . A pitcher is assessed an earned run for each run scored by a baserunner who reached base while batting against that pitcher, whether by hit, base on balls or "walk", or being hit by a pitched ball; an earned run can be charged after the pitcher is relieved if he allows the runner before leaving the game . Runs scored by players who reach base on errors, passed balls, or catcher interference under special circumstances are treated as unearned runs, and do not count towards the pitcher's ERA . </P> <P> Major League Baseball recognizes the player in each league with the lowest earned run average each season . The first ERA champion in the National League was George Bradley; in the National League's inaugural 1876 season, Bradley posted a 1.23 ERA for the St. Louis Brown Stockings, allowing 78 earned runs in 573 innings pitched . The American League was established in 1901, and Hall of Fame pitcher Cy Young led that league with a 1.62 ERA for the Boston Americans during the 1901 season . </P> <P> Over the course of his 17 - year major league career, Lefty Grove led the American League in ERA nine times, with a career single - season low of 2.06 for the 1931 Philadelphia Athletics . Roger Clemens has won the second-most ERA titles, capturing six in the American League and one in the National League . Sandy Koufax led the National League in ERA for five consecutive seasons (1962--1966); Koufax' five awards are the most won consecutively by any player and are tied for the most awards by a player in the National League with Christy Mathewson and Clayton Kershaw . In the American League, Walter Johnson also won five ERA titles, and Pedro Martínez has won a total of five (four American League and one National League) with two different teams . </P>

Who has the best record in the major league