Who holds the single-game strikeout record?

There are two separate lists when discussing which pitcher has the single-game strikeout record, both based on the 18-strikeout threshold. There are two lists: 18 strikeouts in a nine-inning game and 18 strikeouts in extra innings.

The lists are separated because a fair comparison between nine-inning games and extra-inning games is impossible. Extra-inning games, as opposed to nine-inning games, provide pitchers with additional opportunities to record strikeouts.

Tom Cheney is the only pitcher in history to record 21 strikeouts in a single game, however, those strikeouts came after 16 innings with the Washington Senators.

"I told him I didn't want to come out", Cheney said. "Back in those days, you finished what you started."

Cheney threw 228 pitches to record his 21 strikeouts.

"In 1962, Washington Senators pitcher Tom Cheney struck out a record 21 batters. It took him 200+ pitches to do it. Yes, you read that right" - SB Nation

An unspoken benchmark for exceptional performance is 18 strikeouts. Only 20 pitchers in history have struck out 18 batters or more in a nine-inning game. Only three different pitchers struck out 20 batters out of those 20.

Max Scherzer, Kerry Wood, and Roger Clemons (twice) are the only pitchers in history to record 20 strikeouts, which remains the single-game strikeout record through nine innings. MLB Hall of Famer Randy Johnson struck out 20 batters in 2001, and even though the game went into extra innings, he was relieved after nine innings.

"Since 2000 Two Pitchers Have Recorded 20 Strikeout Games: Randy Johnson - 5/8/01, Max Scherzer - 5/11/16. The Most Recent Player To Come Within 3 Strikeouts Of This Incredible Feat Was Chris Sale (5/14/19) Striking Out 17. Can Anyone Reach This Milestone Mark In 2023?" - MLBMuse

Max Scherzer tied the single-game strikeout record on May 11, 2016, for the Washington Nationals against the Detroit Tigers. Scherzer tied the strikeout record by striking out future Hall of Famer Miguel Cabrera, J.D. Martinez, and Ian Kinsler three times apiece.

A look at the career of Tom Cheney, the man who set the single-game strikeout record

While Tom Cheney holds the record for the most strikeouts in a single game, he had a relatively average career. He spent eight seasons in the MLB, pitching for the Washington Senators, Pittsburgh Pirates, and St. Louis Cardinals.

Through eight seasons, Cheney started 71 games, posting a 19-29 record with a 3.77 ERA and 345 strikeouts. He was a member of the World Series champion Pittsburgh Pirates in 1960.