A perfect game is efined 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 only 17 times in major league history.