High Quality Content by WIKIPEDIA articles! 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. 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 20 times in the history of major league baseball—18 times since the modern era began in 1900.