In baseball and softball, a relief pitcher or reliever is a pitcher who enters the game after the starting pitcher is removed due to injury, ineffectiveness, fatigue, ejection, or for other strategic reasons, such as inclement weather delays or pinch hitter substitutions. Relief pitchers are further divided informally into various roles, such as closers, setup men, middle relief pitchers, left/right-handed specialists, and long relievers. Whereas starting pitchers usually rest several days before pitching in a game again due to the number of pitches thrown, relief pitchers are expected to be more flexible and typically pitch more games but with fewer innings pitched. A team's staff of relievers is normally referred to metonymically as a team's bullpen, which refers to the area where the relievers sit during games, and where they warm-up prior to entering the game.
In the early days of Major League Baseball (MLB), substituting a player was not allowed except for sickness or injury. An ineffective pitcher would switch positions with another player on the field. The first relief appearance in the major leagues was in 1876 with Boston Red Caps outfielder Jack Manning switching positions with pitcher Joe Borden. In this early era, relief pitchers changing from a position role to the pitcher's box in this way were often called "change" pitchers. This strategy of switching players between the mound and the outfield is still occasionally employed in modern baseball, sometimes in long extra inning games where a team is running out of players. In 1889, the first bullpen appearance occurred after rules were changed to allow a player substitution at any time. Early relief pitchers were normally starting pitchers pitching one or two innings in between starts. In 1903, during the second game of the inaugural World Series, Pittsburgh's Bucky Veil became the first relief pitcher in World Series history.
Firpo Marberry is credited with being the first prominent reliever. From 1923 to 1935, he pitched in 551 games, 364 of which were in relief. Baseball historian Bill James wrote that Marberry was "a modern reliever—a hard throwing young kid who worked strictly in relief, worked often, and was used to nail down victories." Another reliever, Johnny Murphy, became known as "Fireman" for his effectiveness when inserted into difficult situations ("put out fires") in relief.
Nonetheless, the full-time reliever who was entrusted with important situations was more the exception than the rule at this point. Often, a team's ace starting pitcher was used in between his starts to "close" games. Later research would reveal that Lefty Grove would have been in his league's top three in saves in four different seasons, had that stat been invented at the time.
Gradually after World War II, full-time relievers became more acceptable and standard. The relievers were usually pitchers that were not good enough to be starters. Relievers in the 1950s started to develop oddball pitches to distinguish them from starters. For example, Hoyt Wilhelm threw a knuckleball, and Elroy Face threw a forkball.
Relievers became more respected in the 1970s, and their pay increased due to free agency. All teams began having a closer. The 1980s were the first time in MLB that the number of saves outnumbered complete games. In 1995, there were nearly four saves for every complete game. It is unclear whether the specialization and reliance on relief pitchers led to pitch counts and fewer complete games, or whether pitch counts led to greater use of relievers.
In past decades, the relief pitcher was merely an ex-starter who came into a game upon the injury, ineffectiveness, or fatigue of the starting pitcher. The bullpen was for old starters who had lost the ability to throw effectively. Many of these pitchers would be able to flourish in this diminished role. Those such as Dennis Eckersley, as with many others, actually prolonged their tapering careers and often sparked them to new life. The added rest to their arms as well as the lessened exposure of their abilities became an advantage many would learn to capitalize on. Because these pitchers only faced some batters once a season, the opposing side would have greater difficulty preparing to face relief pitchers.
Recently, being a relief pitcher has become more of a career, rather than a reduced position. Many of today's top prospects are considered mainly for their relief pitching skills. In the quest for a managerial edge, managers as time goes on have carried more pitchers in the bullpen, and used them in more specialized situations. Acknowledgment of the platoon edge has prompted managers to ensure that opposing lefty hitters face as many lefty pitchers as possible, and that the same occur with respect to righty hitters and pitchers. Tony La Russa was particularly well known for making frequent pitching changes on this basis.
When Mike Marshall set the all-time record with 106 games pitched in 1974, he threw 208.1 innings. Currently, although some relievers still do appear in a large number of games per season, the workload for each individual pitcher has been much reduced. Since 2008, Pedro Feliciano has three of the top four seasons in games pitched, with 92, 88 and 86. However, Feliciano only averaged 58 innings pitched during those seasons. The last pitcher to throw 100 or more innings in a season without starting a game was Scott Proctor in 2006.
Pitching staffs on MLB teams have grown from 9 or 10 to as many as 12 or 13 pitchers, due to the increased importance of relief pitching. The staff generally consists of five starting pitchers, with the remaining pitchers assigned as relievers. A team's relief staff usually contains a closer who generally pitches the ninth inning, a setup pitcher who generally pitches the eighth, and a left-handed specialist whose job is to retire left-handed batters. The rest of the bullpen then consists of middle relievers who are used in the remaining situations, and perhaps additional left-handed or right-handed specialists.
The closer is usually the best relief pitcher, followed by the setup man. Players typically get promoted into later-inning roles as they succeed. Relievers were previously more multipurpose before becoming one-inning specialists.
The setup man and closer will normally only be used to preserve a lead, although they may enter to maintain a close game (where the score is tied or if their team is trailing by only a few runs) particularly in the playoffs. If the team is significantly behind going into the eighth or ninth inning and a relief pitcher is required, usually a middle reliever or two will be chosen to soak up innings, while the setup man and closer are saved for the next time they are needed to preserve a win. The proper use of the bullpen is to avoid using an effective reliever on a low-leverage situation, instead saving them as "fireman" for difficult situations.
In 2018, some MLB teams began experimenting with an opener – a pitcher who is normally a reliever that starts the game for an inning or two before yielding to someone who would normally be a starter. One advantage of this approach is that the opener, who is often a hard-throwing specialist, can be called in to face the most dangerous hitters, who are usually near the top of the batting order, the first time they come to bat. Although the opener has only been formally regarded as a relief role in 2018, managers have sporadically used a reliever before a starter. A good example is Game 6 of the 1990 National League Championship Series when Pittsburgh Pirates manager Jim Leyland started a set-up man, Ted Power, in order to keep the Cincinnati Reds from employing their successful platoon (Power pitched 2 1⁄3 innings prior to giving way to lefty starter Zane Smith in the third inning) and the strategy worked in holding the Reds to only two runs; to deceive his opponents Leyland had announced the Game 6 starter at a press conference so that the Reds would set their batting order around Smith.
Between their scheduled starts in the rotation, a starting pitcher can be used on short rest for the bullpen. They are sometimes used as relievers when the stakes are higher, such as a game that could decide the division title or an elimination (winner-take all) playoff game. Regarded as an "universal truth in baseball", "almost every starting pitcher would be better in relief". In the current era, starters are typically used in relief situations either early the postseason prior to their scheduled rotation start, or late in the postseason after their last scheduled start (often with "the ultimatum of a series clincher"). However, the 2018 Boston Red Sox under Alex Cora managed their pitching rotation such that a starter was readily available in the bullpen every playoff game.
A good example is the deciding Game 6 of the 2010 NLCS, where the San Francisco Giants bullpen utilized two starters as well as three regular relievers to get seven scoreless innings. In Game 6 of the 2010 ALCS, manager Joe Girardi was criticized for "managing by formula" in not calling upon ace CC Sabathia and instead going to reliever David Robertson who surrendered several runs that put the game out of reach for the New York Yankees.
Starter Madison Bumgarner recorded the longest save in World Series history, pitching five scoreless innings of relief in a Game 7 3-2 victory of the 2014 edition. In the 2018 World Series, starter Nathan Eovaldi, originally slated to pitch Game 4, was inserted in relief during Game 3 which turned into an 18-inning marathon. In making World Series history, he became the first reliever to throw at least six innings after Rick Rhoden did so in 1977, while Eovaldi's 97 pitches set the record for the most by a reliever (and also 36 more pitches than Rick Porcello who had started that game).
In the clinching Games of the 2018 NLCS and 2018 World Series, respectively, aces Clayton Kershaw (for Kenley Jansen) and Chris Sale (for Craig Kimbrel, indeed the other pitcher warming up besides Sale was another starter, Nathan Eovaldi) pitched the ninth-inning in lieu of their team's regular closer. Neither relief entrance was a high pressure situation as their teams were already leading 5-1 entering the 9th; but it gave Sale the opportunity to get the final outs of the series (Sale also got the first outs of the series when he started the opener).
In games where a blowout is occurring, position players (non-pitchers) may be substituted in to pitch to save the bullpen for the next game. However, this is a rare occurrence as position players are not truly trained as pitchers, and tend to throw with less velocity and/or accuracy. There is also the increased risk of injury, such as Jose Canseco who suffered a season-ending arm injury after pitching 2 innings in a 1993 game. For these reasons, managers will typically only use a position player as a pitcher in a blowout loss, or in order to avoid a forfeit once they have run out of available pitchers. Typically, the position player also pitched at the high school or collegiate level, as smaller roster sizes at amateur levels forced some position players to pitch, with some were recruited in college also as pitchers either as starters or middle relief. Mitch Moreland (Mississippi State), Ryan Rua (Lake Erie College), and J. D. Davis (Cal State Fullerton) all played both position players and pitchers in their collegiate careers, with Rua and Davis both being closers for their college teams.
Cliff Pennington became the first position player in Major League Baseball history to pitch in a postseason game, which was during Game 4 of the 2015 American League Championship Series. The second position player to pitch in the playoffs was Austin Romine during Game 3 of the 2018 American League Division Series.
The Major League Baseball Reliever of the Year Award and The Sporting News Reliever of the Year Award are annually voted on and presented to relievers, with the former being split by league into the "Trevor Hoffman NL Reliever of the Year Award" and the "Mariano Rivera AL Reliever of the Year Award." The Rolaids Relief Man of the Year Award is determined by a statistical formula.
Compared to starting pitchers, most relievers (with the except of closers with large save totals) receive few awards and honors. Historically, setup men were rarely selected to MLB All-Star Games, with the relievers selected usually being closers. A setup man has never won the Cy Young Award or the Major League Baseball Most Valuable Player Award; the highest placements in these respective awards have been achieved by Mariano Rivera who finished third in the voting for the American League (AL) Cy Young Award and twelfth for the AL MVP in 1996, and for the next season he was promoted to closer. Middle reliever Andrew Miller became the first relief pitcher other than a closer to win a League Championship Series Most Valuable Player Award when he was voted the 2016 ALCS MVP.
Setup pitchers typically make less than the MLB average salary. Relief pitchers further down the line may be journeymen as their individual performances may vary greatly, even though their team's relief pitching staff as a whole is overall effective.
The rising importance placed on relief pitchers is evident in the rising star power of the closer. It has gotten to the point where closers are among the biggest stars in the game, with status and salaries on par with starting pitchers. When closers are playing at home, and when they are called into the game to preserve a lead for that last crucial inning or those last couple of outs, many of them trot in from the bullpen to the pitchers mound accompanied by a theme song of their choice. For many years with the Yankees, closer Mariano Rivera entered the game accompanied by Metallica's "Enter Sandman" booming over Yankee Stadium's sound system. When Jonathan Papelbon was with the Red Sox, his entry song was the Dropkick Murphys "Shipping Up to Boston" and Trevor Hoffman entered to the tune of AC/DC's "Hells Bells." 
Six pitchers are currently in the Baseball Hall of Fame chiefly for their accomplishments as relief pitchers: Goose Gossage, Hoyt Wilhelm, Rollie Fingers, Bruce Sutter, Dennis Eckersley and Hoffman. Eckersley, who was considered the first modern closer pitching exclusively in ninth inning situations, also had a significant career as a starting pitcher and even threw a no-hitter in 1977. Another pitcher entering the Hall in 2015, John Smoltz, was primarily a starter, but spent four seasons as a reliever.
Jim Konstanty in 1950 was the first reliever to win the MLB Most Valuable Player Award after a then-record 74 games, 16–7 record, 22 saves, and a 2.66 ERA. Mike Marshall in 1974 was the first reliever to win the Cy Young Award after a record 106 games, 15–12 record, 21 saves, and 208 innings pitched. In 1992, Dennis Eckersley was the first modern closer (first player to be used almost exclusively in ninth inning situations) to win the Cy Young, and since then only one other relief pitcher has won the Cy Young, Éric Gagné in 2003 (also a closer). Three relief pitchers have won both the MVP and Cy Young Awards in one season; Rollie Fingers in 1981, Willie Hernández in 1984, and Eckersley in 1992.
Relievers who have won the Rookie of the Year Award
|1976||National||Butch Metzger||San Diego Padres|
|1980||National||Steve Howe||Los Angeles Dodgers|
|1986||National||Todd Worrell||St. Louis Cardinals|
|1989||American||Gregg Olson||Baltimore Orioles|
|1999||National||Scott Williamson||Cincinnati Reds|
|2000||American||Kazuhiro Sasaki||Seattle Mariners|
|2005||American||Huston Street||Oakland Athletics|
|2009||American||Andrew Bailey||Oakland Athletics|
|2010||American||Neftalí Feliz||Texas Rangers|
|2011||National||Craig Kimbrel||Atlanta Braves|
Relievers who have won the Cy Young Award
|1974||National||Mike Marshall||Los Angeles Dodgers|
|1977||American||Sparky Lyle||New York Yankees|
|1979||National||Bruce Sutter||Chicago Cubs|
|1981||American||Rollie Fingers||Milwaukee Brewers|
|1984||American||Willie Hernández||Detroit Tigers|
|1987||National||Steve Bedrosian||Philadelphia Phillies|
|1989||National||Mark Davis||San Diego Padres|
|1992||American||Dennis Eckersley||Oakland Athletics|
|2003||National||Éric Gagné||Los Angeles Dodgers|
Relievers who have won the Major League Baseball Most Valuable Player Award
|1950||National||Jim Konstanty||Philadelphia Phillies|
|1981||American||Rollie Fingers||Milwaukee Brewers|
|1984||American||Willie Hernández||Detroit Tigers|
|1992||American||Dennis Eckersley||Oakland Athletics|