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In
baseball statistics Baseball statistics play an important role in evaluating the progress of a player or team. Since the flow of a baseball game has natural breaks to it, and normally players act individually rather than performing in clusters, the sport lends itsel ...
, earned run average (ERA) is the average of
earned run In baseball, an earned run is any run that was fully enabled by the offensive team's production in the face of competent play from the defensive team. Conversely, an unearned run is a run that would not have been scored without the aid of an erro ...
s allowed by a
pitcher In baseball, the pitcher is the player who throws ("pitches") the baseball from the pitcher's mound toward the catcher to begin each play, with the goal of retiring a batter, who attempts to either make contact with the pitched ball or draw ...
per nine innings pitched (i.e. the traditional length of a game). It is determined by dividing the number of earned runs allowed by the number of innings pitched and multiplying by nine. Thus, a lower ERA is better. Runs resulting from passed balls or defensive errors (including pitchers' defensive errors) are recorded as
unearned run In baseball, an earned run is any run that was fully enabled by the offensive team's production in the face of competent play from the defensive team. Conversely, an unearned run is a run that would not have been scored without the aid of an error ...
s and omitted from ERA calculations.


Origins

Henry Chadwick is credited with devising the statistic, which caught on as a measure of pitching effectiveness after
relief pitching In baseball and softball, a relief pitcher or reliever is a pitcher who enters the game after the starting pitcher is removed because of fatigue, ineffectiveness, injury, or ejection, or for other strategic reasons, such as inclement weather d ...
came into vogue in the 1900s. Prior to 1900—and, in fact, for many years afterward—pitchers were routinely expected to pitch a complete game, and their
win–loss record In sports, a winning percentage is the fraction of games or matches a team or individual has won. The statistic is commonly used in standings or rankings to compare teams or individuals. It is defined as wins divided by the total number of matc ...
was considered sufficient in determining their effectiveness. After pitchers like
James Otis Crandall James Otis Crandall (October 8, 1887 – August 17, 1951) was a right-handed pitcher and second baseman. He was the first player to be consistently used as a relief pitcher. Consequently, he was given the nickname Doc by Damon Runyon who said ...
and Charley Hall made names for themselves as relief specialists, gauging a pitcher's effectiveness became more difficult using the traditional method of tabulating wins and losses. Some criterion was needed to capture the apportionment of earned-run responsibility for a pitcher in games that saw contributions from other pitchers for the same team. Since pitchers have primary responsibility for striking opposing batters out, they must assume responsibility when a batter they do not retire at the plate moves to base, and eventually reaches home, scoring a run. A pitcher is assessed an earned run for each run scored by a batter (or that batter's
pinch-runner In baseball, a pinch runner is a player substituted for the specific purpose of replacing another player on base. The pinch runner may be faster or otherwise more skilled at base-running than the player for whom the pinch runner has been sub ...
) who reaches base while batting against that pitcher. The
National League The National League of Professional Baseball Clubs, known simply as the National League (NL), is the older of two leagues constituting Major League Baseball (MLB) in the United States and Canada, and the world's oldest extant professional team ...
first tabulated official earned run average statistics in 1912 (the outcome was called "Heydler's statistic" for a while, after then-NL secretary
John Heydler John Arnold Heydler (July 10, 1869 – April 18, 1956) was an American executive in Major League Baseball. After working as a National League (NL) umpire, he was the secretary to the NL president and then became the secretary-treasurer of the NL b ...
), and the
American League The American League of Professional Baseball Clubs, known simply as the American League (AL), is one of two leagues that make up Major League Baseball (MLB) in the United States and Canada. It developed from the Western League, a minor league ...
later accepted this standard and began compiling ERA statistics. Baseball encyclopedias will often display ERAs for earlier years, but these were computed retroactively.
Negro league The Negro leagues were United States professional baseball leagues comprising teams of African Americans and, to a lesser extent, Latin Americans. The term may be used broadly to include professional black teams outside the leagues and it may be ...
pitchers are often rated by ''RA'', or total runs allowed, since the statistics available for Negro league games did not always distinguish between earned and unearned runs.


ERA in different decades

As with
batting average Batting average is a statistic in cricket, baseball, and softball that measures the performance of batters. The development of the baseball statistic was influenced by the cricket statistic. Cricket In cricket, a player's batting average is ...
, the definition of a good ERA varies from year to year. During the
dead-ball era In baseball, the dead-ball era was the period from around 1900 to the emergence of Babe Ruth as a power hitter in 1919, when he hit a then-major league record 29 home runs; only three players since 1890 had even hit 20. This era was characterized ...
of the 1900s and 1910s, an ERA below 2.00 (two earned runs allowed per nine innings) was considered good. In the late 1920s and through the 1930s, when conditions of the game changed in a way that strongly favored hitters, a good ERA was below 4.00; only the highest caliber pitchers, for example
Dazzy Vance Charles Arthur "Dazzy" Vance (March 4, 1891 – February 16, 1961) was an American professional baseball player. He played as a pitcher for five different franchises in Major League Baseball (MLB) in a career that spanned twenty years. Known for ...
or
Lefty Grove Robert Moses "Lefty" Grove (March 6, 1900 – May 22, 1975) was an American professional baseball pitcher. After having success in the minor leagues during the early 1920s, Grove became a star in Major League Baseball with the American League's P ...
, would consistently post an ERA under 3.00 during these years. In the 1960s, sub-2.00 ERAs returned, as other influences such as ballparks with different dimensions were introduced. Starting with the 2019 season, an ERA under 4.00 is again considered good. The single-season record for the lowest ERA is held by Dutch Leonard, who in 1914 had an earned run average of 0.96, pitching 224.2 innings with a win–loss record of 19–5. The all-time record for the lowest single season earned run average by a pitcher pitching 300 or more innings is 1.12, set by
Bob Gibson Robert Gibson (born Pack Robert Gibson; November 9, 1935October 2, 2020) was an American professional baseball pitcher who played 17 seasons in Major League Baseball (MLB) for the St. Louis Cardinals (1959–1975). Nicknamed "Gibby" and "Hoot" ( ...
in 1968. The record for the lowest career earned run average is 1.82, held by
Ed Walsh Edward Augustine "Big Ed" Walsh (May 14, 1881 – May 26, 1959) was an American pitcher and manager in Major League Baseball. From 1906 to 1912, he had several seasons where he was one of the best pitchers in baseball. Injuries shortened his c ...
, who played from 1904 through 1917.


Infinite and undefined

Some players may be listed with infinite ERAs. This can happen if a pitcher allows one or more earned runs without retiring a batter. Several players have registered an infinite ERA for their limited pitching careers in MLB, usually a single appearance. Examples include Bill Ford with the
Boston Bees The Atlanta Braves, a current Major League Baseball franchise, originated in Boston, Massachusetts. This article details the history of the Boston Braves, from 1871 to 1952, after which they moved to Milwaukee, and then to Atlanta. During ...
in 1936 and
Fred Bruckbauer Frederick John Bruckbauer (May 27, 1938 – October 14, 2007) was a relief pitcher in Major League Baseball. Listed at and , Bruckbauer batted and threw right-handed. He was born in New Ulm, Minnesota. Bruckbauer was one of the better pitchers i ...
with the Minnesota Twins in 1961. Outfielder
Vic Davalillo Víctor José Davalillo Romero (born July 30, 1936) is a Venezuelan former professional baseball outfielder. He played for 30 years in the U.S., Mexico, and his homeland, compiling more than 4,100 base hits total. Davalillo (pronounced da-va-L ...
made two pitching appearances with
St. Louis Cardinals The St. Louis Cardinals are an American professional baseball team based in St. Louis. The Cardinals compete in Major League Baseball (MLB) as a member club of the National League (NL) Central division. Since the 2006 season, the Cardinals ha ...
in 1969 and failed to record an out while facing four batters and allowing one run, leaving him with an infinite ERA as a major-league pitcher. An undefined ERA occasionally occurs at the beginning of a baseball season, when a pitcher has yet to appear in any games. It is sometimes incorrectly displayed as zero or as the lowest ranking ERA.


Other external factors


Starters and relievers

At times it can be misleading to judge relief pitchers solely on ERA, because they are charged only for runs scored by batters who reached base while batting against them. Thus, if a relief pitcher enters the game with his team leading by 1 run, with 2 outs and the bases loaded, and then gives up a single which scores 2 runs, he is not charged with those runs. If he retires the next batter (and pitches no more innings), his ERA for that game will be 0.00 despite having surrendered the lead. (He is likely recorded with a blown save.) Starting pitchers operate under the same rules but are not called upon to start pitching with runners already on base. In addition, relief pitchers know beforehand that they will only be pitching for a relatively short while, allowing them to exert themselves more for each pitch, unlike starters who typically need to conserve their energy over the course of a game in case they are asked to pitch 7 or more innings. The reliever's freedom to use their maximum energy for a few innings, or even for just a few batters, helps relievers keep their ERAs down. ERA, taken by itself, can also be misleading when trying to objectively judge starting pitchers, though not to the extent seen with relief pitchers.


Designated hitter rule

The advent of the
designated hitter The designated hitter (DH) is a baseball player who bats in place of another position player, most commonly the pitcher. The position is authorized by Major League Baseball Rule 5.11. It was adopted by the American League in 1973 and later by th ...
rule in the American League in 1973 made the pitching environment significantly different. From then up through 2021, pitchers spending all or most of their careers in the AL had been at a disadvantage in maintaining low ERAs, compared to National League pitchers who could often get an easy out when pitching to the opposition's pitcher, who was usually not a very good batter. Starting in 1997, when teams began playing teams from the other league during the regular season, the DH rule was in effect only when such interleague games are played in an American League park; this was rendered moot after the National League permanently adopted the DH in 2022. This difference between the leagues (the DH) also affected relievers, but not to the same degree. This is because National League relievers actually pitched to pitchers less often than NL starters did for a number of reasons, chiefly because relievers are usually active in later innings when the double switch was available and/or pinch hitters tended to be used in the pitcher's batting spot.


Location

ERA is also affected somewhat by the ballpark in which a pitcher's team plays half its games, as well as the tendency of hometown official scorers to assign errors instead of base hits in plays that could be either. As an extreme example, pitchers for the Colorado Rockies have historically faced many problems, all damaging to their ERAs. The combination of high altitude (5,280 ft or 1,610 m) and a semi-arid climate in
Denver Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the Unit ...
causes fly balls to travel up to 10% farther than at sea level. Denver's altitude and low humidity also reduce the ability of pitchers to throw effective breaking balls, due to both reduced air resistance and difficulty in gripping very dry baseballs. These conditions have been countered to some extent since 2002 by the team's use of
humidor A humidor is a humidity-controlled box or room used primarily for storing cigars, cigarettes, cannabis, or pipe tobacco. Either too much or too little humidity can be harmful to tobacco products; a humidor's primary function is to maintain a ste ...
s to store baseballs before games. These difficult circumstances for Rockies pitchers may not adversely affect their win–loss records, since opposing pitchers must deal with the same problems. Indeed, hometown hurlers have some advantage in any given game since they are physically acclimated to the altitude and often develop techniques to mitigate the challenges of this ballpark. Still, conditions there tend to inflate Rockies' ERAs relative to the rest of the league.


Sabermetric treatment of ERA

In modern baseball,
sabermetrics Sabermetrics, or originally SABRmetrics, is the empirical analysis of baseball, especially baseball statistics that measure in-game activity. Sabermetricians collect and summarize the relevant data from this in-game activity to answer specific ques ...
uses several defense independent pitching statistics (DIPS) including a
Defense-Independent ERA In baseball statistics, Defense-Independent ERA (dERA), created by Voros McCracken, projects what a pitcher's earned run average (ERA) would have been, if not for the effects of defense and luck on the actual games in which he pitched. Method Ver ...
in an attempt to measure a pitcher's ability regardless of factors outside his control. Further, because of the dependence of ERA on factors over which a pitcher has little control, forecasting future ERAs on the basis of the past ERAs of a given pitcher is not very reliable and can be improved if analysts rely on other performance indicators such as strike out rates and walk rates. For example, this is the premise of
Nate Silver Nathaniel Read Silver (born January 13, 1978) is an American statistician, writer, and poker player who analyzes baseball (see sabermetrics), basketball, and elections (see psephology). He is the founder and editor-in-chief of ''FiveThirtyEight' ...
's forecasts of ERAs using his
PECOTA PECOTA, an acronym for ''Player Empirical Comparison and Optimization Test Algorithm'', is a sabermetric system for forecasting Major League Baseball player performance. The word is a backronym based on the name of journeyman major league player Bil ...
system. Silver also developed a "quick" earned run average (QuikERA or QERA) to calculate an ERA from peripheral statistics including strikeouts, walks, and groundball percentage. Unlike
peripheral ERA Peripheral ERA (PERA) is a pitching statistic created by the Baseball Prospectus team. It is the expected earned run average taking into account park-adjusted hits, walks, strikeouts, and home runs allowed. Unlike Voros McCracken's DIPS, hits a ...
or PERA, it does not take into account park effects. Another statistic derived from ERA is
Adjusted ERA Adjustment may refer to: *Adjustment (law), with several meanings *Adjustment (psychology), the process of balancing conflicting needs *Adjustment of observations, in mathematics, a method of solving an overdetermined system of equations *Calibra ...
, also called ERA+, which adjusts a pitcher's ERA to a scale where 100 is average for the league and takes into account the various dimensions and other factors of each ballpark. In
baseball statistics Baseball statistics play an important role in evaluating the progress of a player or team. Since the flow of a baseball game has natural breaks to it, and normally players act individually rather than performing in clusters, the sport lends itsel ...
, runs per nine innings (denoted by R/9 or RA9) is a measure of a
pitcher In baseball, the pitcher is the player who throws ("pitches") the baseball from the pitcher's mound toward the catcher to begin each play, with the goal of retiring a batter, who attempts to either make contact with the pitched ball or draw ...
's effectiveness in preventing runs; calculated as: (9 × runs allowed) / ( innings pitched). In this way, it is different from the ERA in that all runs, rather than only earned runs, are included.


All-time career leaders


Career leaders in the live-ball era (post-1920)

Because of rules changes post-1920, most notably the abolition of the spitball and frequent replacement of soiled or scuffed baseballs, the increased importance of the home run (largely due to
Babe Ruth George Herman "Babe" Ruth Jr. (February 6, 1895 – August 16, 1948) was an American professional baseball player whose career in Major League Baseball (MLB) spanned 22 seasons, from 1914 through 1935. Nicknamed "the Bambino" and "the Su ...
), and the American League's adoption of the
designated hitter rule The designated hitter (DH) is a baseball player who bats in place of another position player, most commonly the pitcher. The position is authorized by Major League Baseball Rule 5.11. It was adopted by the American League in 1973 and later by th ...
, ERAs have been noticeably higher than in the early decades of the sport. This is a list of the lowest ERAs among pitchers that played their entire careers after 1920 (minimum 1,000 innings pitched). Note that four of the top seven (
Clayton Kershaw Clayton Edward Kershaw (born March 19, 1988) is an American professional baseball pitcher for the Los Angeles Dodgers of Major League Baseball (MLB) . He has played for the Dodgers for the entirety of his MLB career. A left-handed starting p ...
,
Jacob deGrom Jacob Anthony deGrom (born June 19, 1988), is an American professional baseball pitcher for the Texas Rangers of Major League Baseball (MLB). He has previously played in MLB for the New York Mets. Prior to playing professionally, deGrom attend ...
,
Whitey Ford Edward Charles "Whitey" Ford (October 21, 1928 – October 8, 2020), nicknamed "the Chairman of the Board", was an American professional baseball pitcher who played his entire 16-year Major League Baseball (MLB) career with the New York Yankees ...
and
Sandy Koufax Sanford Koufax (; born Sanford Braun; December 30, 1935) is an American former left-handed pitcher in Major League Baseball (MLB) who played his entire career for the Brooklyn/Los Angeles Dodgers from 1955 to 1966. He has been hailed as one of t ...
) were primarily starting pitchers.
Hoyt Wilhelm James Hoyt Wilhelm (July 26, 1922 – August 23, 2002), nicknamed "Old Sarge", was an American Major League Baseball pitcher with the New York Giants, St. Louis Cardinals, Cleveland Indians, Baltimore Orioles, Chicago White Sox, California Angel ...
was a reliever for most of his career, while the other two are closers.


See also

*
Catcher's ERA Catcher's ERA (CERA) in baseball statistics is the earned run average of the pitchers pitching when the catcher in question is catching. Its primary purpose is to measure a catcher's game-calling, rather than his effect on the opposing team's run ...
*
Component ERA Component ERA or ERC is a baseball statistic invented by Bill James. It attempts to forecast a pitcher's earned run average (ERA) from the number of hits and walks allowed rather than the standard formula of average number of earned runs per nine ...
* FIP *
Run average In baseball statistics, run average (RA) refers to measures of the rate at which runs are allowed or scored. For ''pitchers,'' the run average is the number of runs—earned or unearned—allowed per nine innings. It is calculated using this formu ...


References

{{DEFAULTSORT:Earned Run Average Pitching statistics