In minor league baseball―a competition hierarchically below the Major League Baseball (MLB)―the record for the most strikeouts (K) in a game is 27. Ron Necciai from Pennsylvania pulled off this feat in a nine inning game on May 13, 1952, while playing for the Bristol Twins against Welch Miners. Impressive indeed! As we graduate to the Major League, competition becomes tougher and records gain more weightage. Most Strikeouts in a MLB Game On September 12, 1962, a right-handed pitcher from Georgia, Tom Cheney created history by striking out 21 batters from the opposition. He pulled off this feat while playing for the Washington Senators against Baltimore Orioles. It was the record for the most strikeouts in a single Major League Baseball regular season game in the history. He struck out 13 Baltimore Orioles in the first nine innings and eventually took his tally to 21 after 16 innings. The game ended with a hard-fought 2 - 1 victory for the Senators. Even though Cheney had to play 16 innings to achieve this feat, it was still a single game, and therefore, the record for most Ks in a single game of Major League Baseball goes to him. Most Ks in a Single Nine Innings MLB Game In baseball history, the record for the most strikeouts in a single game of nine innings is 20. It is held by two players: Roger Clemens from Ohio and Kerry Wood from Texas. In fact, Clemens has achieved this incredible feat twice in his career; 1986 and 1996 seasons respectively. The first instance of 20 strikeouts in a single game was recorded on April 29, 1986, when Roger Clemens, playing for Boston Red Sox, struck out 20 batters of the Seattle Mariners' side. Clemens repeated this amazing feat on September 18, 1996, once again for the Boston Red Sox, but this time against the Detroit Tigers. Clemens was the only player to strikeout 20 batters in a single nine innings game until Chicago Cubs pitcher, Kerry Wood joined him with 20 strikeouts against Houston Astros on May 6, 1998. While Clemens and Woods have the most number of strikeouts in a single nine innings games to their credit, Randy Johnson, David Cone, Nolan Ryan, Tom Seaver, Steve Carlton, Hugh Daily, and Charlie Sweeney have come close with 19 strikeouts each. Most Strikeouts in a Playoff Game In Major League Baseball, the games which are played after the regular season are known as the post-season games instead of playoffs. The term 'playoffs', on the other hand, is reserved for a game that determines which of the two teams tied at the same spot would qualify for the post-season games. The record for the most strikeouts in a post-season game is held by Robert 'Bob' Gibson for his 17 strikeouts in Game 1 of the 1968 World Series. Gibson represented defending champions St. Louis Cardinals in this World Series game against the Detroit Tigers. If there is no restriction on the number of innings, the record is held by Tom Cheney for his 21 strikeouts against Baltimore Orioles. On the other hand, if you restrict the number of innings to nine, this record is held jointly by Roger Clemens and Kerry Wood with 20 strikeouts each. While that was about the pitchers, the record for the most strikeouts for a batter (with the innings factor coming into play yet again) is held by 8 baseball players who have been struck out six times in a 9+ innings game and 46 players having struck out five times in a 9 innings game.