Most strikeouts in a game
20 in nine innings, 4 times: Max Scherzer (2016), Kerry Wood (1998) and Roger Clemens (1986, 1996).
3 pitchers have struck out 20 in a nine-inning game, Roger Clemens twice. In any game, the record is Tom Cheney's 21 in 16 innings for the Washington Senators on September 12, 1962.
18 or more in a nine-inning game
More than once in nine innings: Randy Johnson 3 times, Roger Clemens 3 times, Nolan Ryan 2 times and Sandy Koufax 2 times.
Regular season. Team names as they were that day; the score is the pitcher's team first.
18 or more in an extra-inning game
Kept apart, as the record book keeps them: a pitcher who works 16 innings gets more than nine innings' worth of batters.
Questions
What is the most strikeouts in a nine-inning game?
20, 4 times: Max Scherzer for the Washington Nationals against the Detroit Tigers on May 11, 2016, Kerry Wood for the Chicago Cubs against the Houston Astros on May 6, 1998, Roger Clemens for the Boston Red Sox against the Detroit Tigers on September 18, 1996 and Roger Clemens for the Boston Red Sox against the Seattle Mariners on April 29, 1986.
What is the most strikeouts in any MLB game?
21, by Tom Cheney of the Washington Senators in 16 innings against the Baltimore Orioles on September 12, 1962.
Who has struck out 19 in a game?
Randy Johnson (twice in 1997), David Cone (1991), Nolan Ryan (1974), Tom Seaver (1970), Steve Carlton (1969), Hugh Daily (1884) and Charlie Sweeney (1884) in nine innings.
Who has the most 18-strikeout games?
Randy Johnson and Roger Clemens, 3 each in nine innings.
When was the last 18-strikeout game?
Max Scherzer, 20 for the Washington Nationals against the Detroit Tigers on May 11, 2016.