A
perfect game is defined by
Major League Baseball as a game in which a
pitcher (or combination of pitchers) pitches a
victory that lasts a minimum of nine
innings and in which no opposing player reaches
base.
[1] Thus, the pitcher (or pitchers) 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". The feat has been achieved only 17 times in major league history.
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. Weather-shortened contests in which a team has no baserunners and games in which a team reaches first base only in
extra innings do not qualify as official under the present definition. The first confirmed use of the term "perfect game" was in
1908; the current official definition of the term was formalized in
1991. Although it is possible for multiple pitchers to combine for a perfect game (as has happened nine times at the major league level for a no-hitter), to date every major league perfect game has been a complete game by just a single pitcher.
[2]