In baseball, a perfect game is a game in which one or more pitchers complete a minimum of nine innings with no batter from the opposing team reaching any base. To achieve a perfect game, a team must not allow any opposing player to reach base by any means: no hits, walks, hit batsmen, uncaught third strikes, catcher's or fielder's interference, or fielding errors; in short, "27 up, 27 down" (for a nine-inning game).
A perfect game, by definition, is also a no-hitter, a win, and a shutout. A fielding error that does not allow a batter to reach base, such as a misplayed foul ball, does not spoil a perfect game. Games that last fewer than nine innings, regardless of cause, in which a team has no baserunners do not qualify as perfect games. Games in which a team reaches first base only in extra innings also do not qualify as perfect games.
The first known use of the term perfect game was in 1908; its current definition was formalized in 1991. In Major League Baseball (MLB), the feat has been achieved 23 times – 21 times since the modern era began in 1901, most recently by Félix Hernández of the Seattle Mariners on August 15, 2012. Although it is possible for several pitchers to combine for a perfect game (which has happened 17 times in MLB no-hitters), every MLB perfect game so far has been thrown by a single pitcher. Nippon Professional Baseball's 2007 Japan Series ended with a combined perfect game.
The first known occurrence of the term perfect game in print was in 1908. I. E. Sanborn's report for the Chicago Tribune about Addie Joss's performance against the White Sox calls it "an absolutely perfect game, without run, without hit, and without letting an opponent reach first base by hook or crook, on hit, walk, or error, in nine innings". Several sources have claimed that the first recorded usage of perfect game was by Ernest J. Lanigan in his Baseball Cyclopedia, made in reference to Charlie Robertson's 1922 perfect game. The Chicago Tribune came close to the term in describing Lee Richmond's game for Worcester in 1880: "Richmond was most effectively supported, every position on the home nine being played to perfection." Similarly, in writing up John Montgomery Ward's 1880 perfect game, the New York Clipper described the "perfect play" of Providence's defense.
There has been one perfect game in the World Series, thrown by Don Larsen for the New York Yankees against the Brooklyn Dodgers on October 8, 1956. By coincidence, Larsen was in attendance when Yankee pitcher David Cone threw a perfect game in 1999 on the same day that Larsen and Yogi Berra (the catcher in the 1956 perfect game) were invited to do the ceremonial first pitch.
Ron Hassey is the only catcher in MLB history to have caught more than one perfect game (his first was with pitcher Len Barker in 1981 and his second was with pitcher Dennis Martínez in 1991).
The most recent perfect game for MLB was on August 15, 2012, Félix Hernández of the Seattle Mariners fought against the Tampa Bay Rays. He struck out the side twice and struck out twelve total batters in a 1–0 victory.
The most recent perfect game was thrown by Rōki Sasaki of the Chiba Lotte Marines in the Nippon Professional Baseball (NPB) on April 10, 2022. He struck out 19 batters with 13 strikeouts in a row, which broke the NPB record for consecutive strikeouts and tied the record for total strikeouts in the same game.
As of 2021, the Major League Baseball definition of a perfect game is largely a side effect of the decision made by the major leagues' Committee for Statistical Accuracy on September 4, 1991, to redefine a no-hitter as a game in which the pitcher or pitchers on one team throw a complete game of nine innings or more without surrendering a hit. That decision removed a number of games that had long appeared in the record books: those lasting fewer than nine innings, and those in which a team went hitless in regulation but then got a hit in extra innings. The definition of perfect game was made to parallel this new definition of the no-hitter, in effect substituting "baserunner" for "hit". As a result of the 1991 redefinition, for instance, Harvey Haddix does not receive credit for a perfect game or a no-hitter for his performance on May 26, 1959, when he threw 12 perfect innings against the Milwaukee Braves before a batter reached in the 13th.
A rule change in effect for the 2020 through 2022 seasons awarded the offensive team a free runner on second base each half-inning during extra innings. This rule opened the possibility of a team scoring a run (batting in the free baserunner on a sacrifice fly, for example) without any player ever reaching first base. This would still have been recorded as a perfect game according to MLB's official record-keeper, the Elias Sports Bureau, since an automatic runner is not a batter who reached base safely. Another rule change effective for the same two seasons stipulated that games that are part of doubleheaders only last seven innings. Such a game in which one team did not reach first base would not have been credited as a perfect game (similar to weather-shortened games). However, if such a doubleheader game were to have at least two extra innings and one team still did not reach first base, then the game would have been credited as a perfect game. During those two seasons, no potential perfect games were affected. Both rule changes were expected to be reversed prior to the 2022 season; however, the extra innings rule did return while doubleheaders reverted back to a full nine-inning length.
On April 11, 2021, University of North Texas softball pitcher Hope Trautwein threw a perfect game, facing 21 batters and striking out all 21. It was the first seven-inning perfect game with every out being a strikeout in NCAA Division I history.
The only perfect game thrown in a Little League World Series championship was by Ángel Macías of the Monterrey, Mexico, team in 1957.
In Nippon Professional Baseball (NPB) the first perfect game was thrown by Hideo Fujimoto of the Giants on June 28, 1950, against the Nishi Nippon Pirates.
On April 10, 2022, Chiba Lotte Marines pitcher Rōki Sasaki threw a perfect game in which he tied an existing NPB record by striking out 19 batters, and set a new record by striking out 13 consecutive batters. Sasaki compiled a game score of 106, surpassing the 105 for Kerry Wood's 20 strikeout game from the 1998 Major League Baseball season, which was the highest MLB game score since the end of the baseball color line.