New York Yankee’s Don Larsen pitched the only perfect game in a World Series; one of only 17 perfect games in MLB history.
A perfect game in Major League Baseball is a game in which a pitcher (or combination of pitchers) pitches a victory that lasts a minimum of nine innings and no opposing batter reaches base. To achieve a perfect game, a team must not allow an opposing player to reach base by any means, including hits, walks, hit batsmen, or fielding errors; in short, “27 up, 27 down” (for a nine-inning game). The feat has been achieved 23 times in MLB history – 21 times since the modern era began in 1900, most recently by Félix Hernández of the Seattle Mariners on August 15, 2012. A perfect game is also a no-hitter 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. 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 perfect games under the present definition.
Read more – Source