What's the most strikeouts ever thrown by a pitcher in a single game?

The record for most strikeouts by a pitcher in a single nine-inning game is 20, a mark that has been achieved twice in Major League Baseball history. Roger Clemens was the first to accomplish this feat, doing so on April 29, 1986, when he struck out 20 Seattle Mariners batters while pitching for the Boston Red Sox. Clemens was just 23 years old at the time and threw a complete game, allowing only three hits in a 3-1 victory. He later tied his own record on September 18, 1996, when he again struck out 20 batters, this time against the Detroit Tigers. Kerry Wood of the Chicago Cubs then matched the record on May 6, 1998, in one of the most dominant pitching performances in baseball history. Wood struck out 20 Houston Astros batters in a one-hit shutout, and he did not walk a single batter. Wood was only 20 years old at the time and had been in the major leagues for just a handful of starts. Many baseball analysts consider Wood's game to be arguably the greatest single pitching performance ever, given his age, the near-perfect nature of the outing, and the sheer dominance he displayed against a solid Houston lineup. If you expand beyond nine-inning games, Tom Cheney of the Washington Senators set the all-time record for strikeouts in a single game by fanning 21 Baltimore Orioles batters on September 12, 1962, but that game went 16 innings, which is why it stands apart from the standard nine-inning record. Cheney's performance remains the overall single-game record regardless of game length, though it is often noted separately because of the extra innings involved. In more recent history, Max Scherzer has come close to the nine-inning record on multiple occasions, striking out 17 or more batters in several games throughout his career, but he never quite reached 20. Randy Johnson, Nolan Ryan, and Sandy Koufax were also among the most prolific strikeout pitchers in history and had numerous games with very high strikeout totals, though none surpassed the 20-strikeout mark in a nine-inning contest. The combination of pure velocity, movement, and command required to strike out 20 batters in nine innings makes it one of the rarest and most impressive individual achievements in all of professional sports, which is why the record has stood for decades and is considered one of the most difficult marks in baseball to surpass.