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
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.