Adjusted ERA+

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

Baseball-Reference.com originally calculated it as:

${\displaystyle {\mathit {ERA+}}=100\cdot {{\mathit {lgERA}} \over {\mathit {ERA}}}\cdot {\mathit {PF}}}$

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.

Today, they calculate it as:[1]

${\displaystyle {\mathit {ERA+}}=100\cdot (2-{{\mathit {ERA}} \over {\mathit {lgERA}}}\cdot {1 \over {\mathit {PF}}})}$

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 be used to account for this misleading impression.

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.[2] 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, sixth highest since 1900. 1968 was the last year that Major League Baseball employed the use of a pitcher's mound higher than 10 inches.[3]

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.[4] 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 2019 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).[5] 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 159 3 Pedro Martínez 154 4 Jim Devlin 150 5 Lefty Grove 148 T-6 Walter Johnson 147 Hoyt Wilhelm T-8 Dan Quisenberry 146 Smoky Joe Wood 10 Ed Walsh 145 11 Roger Clemens 143 T-12 Addie Joss 142 Brandon Webb 14 Trevor Hoffman 141 15 Kid Nichols 140 16 Mordecai Brown 139 T-17 John Franco 138 Chris Sale Cy Young T-20 Johan Santana 136 Bruce Sutter T-22 Pete Alexander 135 Christy Mathewson Randy Johnson Rube Waddell

Single Season Leaders Rank Player Adjusted ERA+ Year Team 1 Rollie Fingers 333 1981 Milwaukee Brewers 2 Tim Keefe 293 1880 Troy Trojans 3 Pedro Martínez 291 2000 Boston Red Sox 4 Dutch Leonard 282 1914 Boston Red Sox 5 Greg Maddux 271 1994 Atlanta Braves 6 Greg Maddux 260 1995 Atlanta Braves 7 Walter Johnson 259 1913 Washington Senators 8 Bob Gibson 258 1968 St. Louis Cardinals 9 Mordecai Brown 253 1906 Chicago Cubs 10 Pedro Martínez 243 1999 Boston Red Sox 11 Walter Johnson 240 1912 Washington Senators 12 Christy Mathewson 230 1905 New York Giants 13 Dwight Gooden 229 1985 New York Mets 14 Roger Clemens 226 2005 Houston Astros 15 Pete Alexander 225 1915 Philadelphia Phillies T-16 Christy Mathewson 222 1909 New York Giants Roger Clemens 1997 Toronto Blue Jays T-18 Cy Young 219 1901 Boston Americans Pedro Martínez 1997 Montreal Expos 20 Denny Driscoll 218 1882 Pittsburgh Alleghenys 21 Lefty Grove 217 1931 Philadelphia Athletics

References

1. Forman, Sean. "We Goofed: ERA+ numbers » Baseball-Reference Blog » Blog Archive". www.baseball-reference.com. Retrieved 1 August 2016.
2. 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.
3. Baseball Trivia (General) - Pitchers mound Archived 2009-04-18 at the Wayback Machine, allexperts.com.
4. Baseball Reference career ERA+ leaders, accessed October 21, 2013 (after the 2013 regular season, with Rivera having pitched his last game, had his number retired by the Yankees, but Baseball Reference not yet having marked him as retired on their site). Also the source for the corresponding table.
5. "Official Rules: 10.00 The Official Scorer". Major League Baseball. Retrieved 15 October 2016.