Relief pitcher in the context of "Shota Imanaga"

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 a walk. In the defensive numbering system used in baseball, the pitcher is assigned the number 1. The pitcher is often considered the most important player on the defensive side of the game, and as such is situated at the right end of the defensive spectrum. There are many different types of pitchers, such as the starting pitcher, relief pitcher, middle reliever, lefty specialist, setup man, and the closer.

Traditionally, the pitcher also bats. Starting in 1973 with the American League and spreading to further leagues throughout the 1980s and 1990s, the hitting duties of the pitcher have generally been given over to the position of designated hitter, a cause of some controversy. The National League adopted the designated hitter in 2022; as of 2025, the Japanese Central League is the highest level of competition to not use the designated hitter position.

In baseball, a no-hitter or no-hit game is a game in which a team does not record a hit through conventional methods. Major League Baseball (MLB) officially defines a no-hitter as a completed game in which a team that batted in at least nine complete innings recorded no hits. A pitcher who prevents the opposing team from achieving a hit is thereby said to have "thrown a no-hitter". In most cases, no-hitters are recorded by a single pitcher who throws a complete game; one thrown by two or more pitchers is a combined no-hitter.

A no-hitter is a rare accomplishment for a pitcher or pitching staff—only 326 have been thrown in MLB history since 1876, an average of about two per year. The most recent major league no-hitter, a combined no-hitter, was thrown by starter Shota Imanaga and relief pitchers Nate Pearson and Porter Hodge of the Chicago Cubs against the Pittsburgh Pirates on September 4, 2024, while the most recent no-hitter by a single pitcher was thrown by Blake Snell of the San Francisco Giants against the Cincinnati Reds on August 2, 2024.

In baseball, a middle reliever, or middle relief pitcher, is a relief pitcher who typically pitches during the fifth, sixth, and seventh innings of a standard baseball game. In leagues with no designated hitter, such as in the National League before 2022 and the Japanese Central League, a middle reliever often comes in after the starting pitcher has been pulled in favor of a pinch hitter. Middle-relief pitchers are usually tasked to pitch one, two, or three innings. Several factors determine this, such as who’s winning, the score, eligible bullpen pitchers remaining, the importance of the current game, etc. After the middle relief pitcher has completed his portion, they are normally replaced in later innings by a left/right-handed specialist, setup pitcher, and/or lastly a closer. When they’re replaced, it is partly due to deprivation of stamina and/or effectiveness but also characteristics, such as pitch arsenal, speed of pitches, which arm they throw with, and who’s up to bat next for the opposing team. Middle relievers may pitch in these later innings, especially during games tied or close in score.

In baseball, a left-handed specialist (also known as lefty specialist) is a relief pitcher who throws left-handed and specializes in pitching to left-handed batters, weak right-handed batters, and switch-hitters who bat poorly right-handed. Because baseball practices permanent substitution, these pitchers frequently pitch to a very small number of batters in any given game (historically, often only one), and rarely pitch to strictly right-handed batters. Most Major League Baseball (MLB) teams have several left-handed pitchers on their rosters, at least one of whom is a left-handed specialist. A left-handed specialist is sometimes called a LOOGY (or Lefty One-Out GuY), coined by John Sickels, and may be used pejoratively.

In baseball, a setup man (or set-up man, also sometimes referred to as a setup pitcher or setup reliever) is a relief pitcher who regularly pitches before the closer. They commonly pitch the eighth inning, with the closer pitching the ninth.

As closers were reduced to one-inning specialists, setup men became more prominent. Setup pitchers often come into the game with the team losing or the game tied. They are usually the second best relief pitcher on a team, behind the closer. After closers became one-inning pitchers, primarily in the ninth inning, setup pitchers became more highly valued. A pitcher who succeeds in this role is often promoted to a closer, and often fill in for the regular closer when the regular closer needs a day off for rest. Setup men are paid less than closers and mostly make less than the average Major League salary.

In baseball, a closing pitcher, more frequently referred to as a closer (abbreviated CL), is a relief pitcher who specializes in getting the final outs in a close game when his team is in the lead. A closer who successfully gets the final outs for their team in the final inning of a game is recorded as a save in baseball statistics. The role is often assigned to a team's best reliever. Before the 1990s, pitchers in similar roles were referred to as a fireman and stopper. Closers typically specialize in a breaking ball of some sort in order to minimize the risk of home runs late in games, and to deceive batters into swinging away from the strike zone.

In Major League Baseball (MLB), some closers have been noted for their use of entrance music when they jog out to the mound to warm up, often to excite the fans and to intimidate the at-bat. For example, the San Diego Padres of the National League (NL) played the song "Hells Bells" by AC/DC for closer Trevor Hoffman, and the New York Yankees of the American League (AL) played "Enter Sandman" by Metallica for closer Mariano Rivera.

In baseball, a complete game (CG) is the act of a pitcher pitching an entire game without the benefit of a relief pitcher. A pitcher who meets this criterion will be credited with a complete game regardless of the number of innings played—pitchers who throw an entire official game that is shortened by rain will still be credited with a complete game, while starting pitchers who are relieved in extra innings after throwing nine or more innings will not be credited with a complete game. A starting pitcher who is replaced by a pinch hitter in the final half inning of a game will still be credited with a complete game.

Complete games have become increasingly rare over the course of baseball history. In the early 20th century, pitchers completed almost all of the games they started, and they were generally expected to do so. In modern baseball, the feat is much more rare. Since 1975, no pitcher has thrown 30 or more complete games in a season; in the 21st century, only twice has any pitcher thrown 10 or more complete games in a season.