Ask Marilyn ® by Marilyn vos Savant is a column in Parade Magazine, published by PARADE, 711 Third Avenue, New York, NY 10017, USA. According to Parade, Marilyn vos Savant is listed in the "Guinness Book of World Records Hall of Fame" for "Highest IQ."
In her Parade Magazine column of April 6, 1997, Marilyn reports that in a complete major league baseball game, not counting exceptions such as a rain out, the minimum number of pitches thrown would be 25 for a visiting pitcher and 27 for a home pitcher.
Using the nuances of major league baseball rules, Marilyn's answer should have been 9 pitches from either pitcher. How do you pitch only 9 pitches in a complete 9 inning game when there would be up to 27 batters? Here's how. With the first pitch of each inning, the pitcher hits the batter who then advances to first base. This counts as 1 pitch. The next batter is pitched to but interferes with the catcher who attempts to throw the runner out. This doesn't count as a pitch due to the batters interference with the catcher. The batter is called out by the umpire, is credited with an at bat, but the pitcher is not credited with another pitch. Repeat this scenario each inning for both teams. Since only the first pitch of each inning counts as a pitch, only 9 pitches could be thrown by the home team pitcher if the home team wins and 9 pitches would be thrown by the losing pitcher when the first batter of the bottom of the 9th inning hits a home run.
I know this is a little contrived, but this scenario fits the rule book.
The 25th pitch from the visiting pitcher doesn't eliminate the need for the bottom of the ninth; that one pitch and home run themselves constitute the bottom of the ninth.
Regarding the minimum number of pitches for a complete game, the rules of Major League Baseball state:
8.04 When the bases are unoccupied, the pitcher shall deliver the ball to the batter within 20 seconds after he receives the ball. Each time the pitcher delays the game by violating this rule, the umpire shall call "Ball." The intent of this rule is to avoid unnecessary delays. The umpire shall insist that the catcher return the ball promptly to the pitcher, and that the pitcher take his position on the rubber promptly. Obvious delay by the pitcher should instantly be penalized by the umpire.
It is therefore possible for a pitcher to delay four times in a row, walking the batter to first base, and then pick him off. If he does this for every batter, he can "pitch" a full game (a no-hitter, incidentally) without ever actually delivering a pitch. Now, it is inconceivable that a pitcher would do that in actual play, or that a manager or umpire would allow it to happen, but it is allowable under the rules.