Adjusted ERA+, often simply abbreviated to ERA+ or ERA plus, is a pitching statistic in baseball. It adjusts a pitcher's earned run average (ERA) according to the pitcher's ballpark (in case the ballpark favors batters or pitchers) and the ERA of the pitcher's league.

Formula ERA+ is calculated as:

Where ERA is the pitcher's ERA, lgERA is the average ERA of the league, and PF is the park factor of the pitcher in question.

This formula is now standard, although Baseball-Reference.com briefly used a different formula which took values strictly between 0 and 200 instead of between 0 and infinity, but the current website shows values above 200 so it is clearly no longer in use:

The average ERA+ is set to be 100; a score above 100 indicates that the pitcher performed better than average, while below 100 indicates worse than average. For instance, imagine the average ERA in the league is 4.00: if pitcher A has an ERA of 4.00 but is pitching in a ballpark that favors hitters, his ERA+ will be over 100. Likewise, if pitcher B has an ERA of 4.00 but pitches in a ballpark favoring pitchers, then his ERA+ will be below 100.

As a result, ERA+ can be used to compare pitchers across different run environments. In the above example, while ERA will lead one to believe that both pitchers pitched at the same level due to their ERAs being equivalent, ERA+ indicates that pitcher A performed better than pitcher B. ERA+ can thus be used to neutralize the effects of some well-known advantages and disadvantages on pitchers' ERA scores.

Leaders

Pedro Martínez holds the modern record for highest ERA+ in a single season; he posted a 1.74 ERA in the 2000 season while pitching in the American League, which had an average ERA of 4.92, which gave Martínez an ERA+ of 291.Single season awards require a minimum of one inning pitched for each game played (thus usually 162 IP in today's game). Thus closers and other relievers will not generally acquire enough innings pitched to qualify. While Bob Gibson has the lowest ERA in modern times (1.12 in the National League in 1968), the average ERA was 2.99 that year (the so-called Year of the Pitcher) and so Gibson's ERA+ is 258, eighth highest since 1900. 1968 was the last year that Major League Baseball employed the use of a pitcher's mound at ; after that season it was lowered to .Baseball Trivia (General) - Pitchers mound , allexperts.com.

The career record for ERA+ (with a minimum of 1,000 innings pitched) is held by Mariano Rivera, a closer whose career ERA+ is 205. Upon retirement in 2013, with an ERA+ of 194 in his final season, Rivera's career record of 205 surpassed the record among retired players of 154, held by Martínez, bumping Jim Devlin, a pitcher in the 1870s, to third with 151.Baseball Reference career ERA+ leaders, accessed June 6, 2021. Also the source for the corresponding table. Among qualifying pitchers, Pedro Martínez has the most separate seasons with an ERA+ over 200, with five, and the most consecutive 200 ERA+ seasons (4), though the closer Rivera, with too few innings each year to qualify officially, has surpassed 200 ERA+ in 13 seasons of his 19 seasons, including 4 consecutive seasons twice and 5 consecutive seasons once and also surpassing 300 in 2004 and again in 2008. Roger Clemens topped a 200 ERA+ three times, and Greg Maddux had two such seasons.

Players in bold are active as of the end of the 2020 season and have not announced their retirement.

Single-season leaders include only pitchers eligible for the ERA title (a pitcher must throw a minimum of one inning per game scheduled for his team during the season to qualify for the ERA title). Only pitchers with 1,000 or more innings pitched are shown in the career leader list.

+Career leaders Rank Player Adjusted ERA+ 1 Mariano Rivera 205 2 Clayton Kershaw 157 3 Jacob deGrom 155 4 Pedro Martínez 154 5 Jim Devlin 150 6 Lefty Grove 148 T-7 Walter Johnson 147 Hoyt Wilhelm T-9 Dan Quisenberry 146 Ed Walsh Smoky Joe Wood T-12 Roger Clemens 143 Addie Joss 14 Brandon Webb 142 15 Trevor Hoffman 141 16 Chris Sale 140 17 Kid Nichols 139 T-18 Mordecai Brown 138 John Franco Cy Young T-21 Christy Mathewson 136 Johan Santana Bruce Sutter T-24 Pete Alexander 135 Randy Johnson Corey Kluber Rube Waddell

+Single-season leadersRank Player Adjusted ERA+ Year Team1Tim Keefe 293 1880 Troy Trojans2Pedro Martínez 291 2000 Boston Red Sox3Shane Bieber 281 2020 Cleveland Indians4Dutch Leonard 279 1914 Boston Red Sox5Trevor Bauer 276 2020 Cincinnati Reds6Greg Maddux 271 1994 Atlanta Braves7Greg Maddux 260 1995 Atlanta Braves8Walter Johnson 259 1913 Washington Senators9Bob Gibson 258 1968 St. Louis Cardinals10Mordecai Brown 253 1906 Chicago Cubs T-11Pedro Martínez 243 1999 Boston Red SoxWalter Johnson 1912 Washington Senators13Christy Mathewson 233 1905 New York Giants14Dwight Gooden 229 1985 New York Mets15Roger Clemens 226 2005 Houston Astros16Pete Alexander 225 1915 Philadelphia Phillies T-17Christy Mathewson 224 1909 New York GiantsDallas Keuchel 2020 Chicago White Sox T-19Roger Clemens 222 1997 Toronto Blue JaysZack Greinke 2015 Los Angeles Dodgers

References