Perfect game

A perfect game is defined by Major League Baseball as a game in which a pitcher pitches a complete game victory that lasts a minimum of nine innings and in which no opposition player reaches first base. Thus, the pitcher cannot allow any hits, walks, hit batsmen, or any opposing player to reach base safely for any other reason—in short, "27 up, 27 down."

By definition, a perfect game must be both a no-hitter and a shutout. Since the pitcher cannot control whether or not his teammates commit any errors, the pitcher must be backed up by solid fielding to pitch a perfect game. An error that does not allow a baserunner, such as a misplayed foul ball, does not spoil a perfect game. Several pitching performances regarded popularly as perfect games do not qualify as official under the present definition, among them weather-shortened games that featured no baserunners by one team and games in which a team reached first base only in extra innings. The first confirmed recorded use of the term "perfect game" was in 1908; the current official definition of the term was formalized in 1991.

Over the past 130 years of Major League Baseball history, there have been only 17 official perfect games by the current definition (approximately one every eight years). In sum, a perfect game is thrown once in about every 20,000 major league contests. For comparison, more people have orbited the moon than have pitched a Major League Baseball perfect game.