In baseball, a strikeout occurs when a pitcher throws three strikes to a batter during his time at bat. Only three pitchers have struck out 20 batters in a single game. Most recent was Max Scherzer, Roger Clemens and then rookie Kerry Wood. Twenty different pitchers have struck out at least 18 batters in a single nine-inning Major League Baseball (MLB) game, the most recent being Max Scherzer of the Washington Nationals on May 11, 2016. Four players have accomplished the feat more than once in their career; no player has ever struck out more than 20 batters in a nine-inning game. Charlie Sweeney was the first player to strike out 18 batters in a single game, doing so for the Providence Grays against the Boston Beaneaters on June 7, 1884. In spite of this, Bob Feller is viewed as the first pitcher to accomplish the feat, since his then-record 18 strikeouts was the first to occur during the 20th century and the live-ball era.
Out of the 20 pitchers who have accomplished the feat, 15 were right-handed and five pitched left-handed. Five of these players have played for only one major league team. Six pitchers—Steve Carlton, Roger Clemens, Randy Johnson, Nolan Ryan, Tom Seaver, and Max Scherzer—are also members of the 3,000 strikeout club. Sweeney has the fewest career strikeouts in the group with 505, while Nolan Ryan, with 5,714, struck out more batters than any other pitcher in major league history. Bill Gullickson and Kerry Wood are the only rookies to have achieved the feat.
Of the eleven players eligible for the Baseball Hall of Fame who have struck out 18 batters in a game, six have been elected; all six were elected on the first ballot. Players are eligible for the Hall of Fame if they have played in at least 10 major league seasons and have either been retired for five seasons or deceased for at least six months.
Players
thumb|upright|[[Bob Feller was the first player to achieve 18 strikeouts in a game during the 20th century.]]
thumb|upright|[[Sandy Koufax was the first pitcher to achieve multiple games with 18 strikeouts, recording two in his career.|alt=A smiling man in a white baseball jersey and dark baseball cap with an interlocked white "LA" on the front.]]
thumb|upright|[[Kerry Wood tied Roger Clemens' major league record of 20 strikeouts in a nine-inning game on May 6, 1998.|alt=A man sporting a goatee and wearing a dark blue baseball cap with "C" in the middle, a pinstriped jersey and black Nike cleats delivers a pitch.]]
thumb|upright|[[Max Scherzer tied Kerry Wood and Roger Clemens' major league record of 20 strikeouts in a nine-inning game in 2016.|alt=A man in white pants and a navy blue baseball jersey with "Nationals" written across the front throws a pitch.]]
{| class="wikitable"
|+Key
!scope="row"|Pitcher
|Name of the pitcher
|-
!scope="row"|Date
|Date of the game
|-
!scope="row"|Team
|The pitcher's team
|-
!scope="row"|Opposing team
|The team against whom the pitcher struck out 18 players
|-
!scope="row"|Score
|Final score of the game, with the pitcher's team score listed first
|-
!scope="row"|Strikeouts
|Number of strikeouts the pitcher recorded
|-
!scope="row"|Career Ks
|Career strikeouts
|-
!scope="row" style="background:#ffb;"|
|Elected to the Baseball Hall of Fame
|-
!scope="row" style="background:#cfecec;"|*
|Player is active
|-
!scope="row" style="text-align:center; background-color: #ffbbbb"|
|Indicates the player's team lost the game
|}
MLB pitchers with 18 strikeouts in a nine-inning game
{| class="wikitable sortable plainrowheaders" style="text-align:center;"
|+MLB pitchers with 18 strikeouts in a nine-inning game (sorted by number of strikeouts, then chronologically)
!scope="col"|Pitcher
!scope="col"|Date
!scope="col"|Team
!scope="col"|Opposing team
!scope="col"|Score
!scope="col"|Strikeouts
!scope="col"|Career Ks
!scope="col" class="unsortable"|Refs
|-
! scope="row" style="text-align:center; background:#cfecec;"|
|||Washington Nationals||Detroit Tigers||3–2|| rowspan="4" |20||3,407||
|-
! rowspan="2" scope="row" style="text-align:center" |
||| rowspan="2" |Boston Red Sox||Detroit Tigers||4–0||4,672||
|-
|||Seattle Mariners||3–1||4,672||
|-
! rowspan="2" scope="row" style="text-align:center; background:#ffb;" |
||| rowspan="2" |Seattle Mariners||Chicago White Sox||5–0|| rowspan="8" |19||4,875||
|-
|||Oakland Athletics||bgcolor="#ffbbbb"|1–4||4,875||
|-
!scope="row" style="text-align:center"|
|||New York Mets||Philadelphia Phillies||7–0||2,668||
|-
! scope="row" style="text-align:center; background:#ffb;"|
|||California Angels||Boston Red Sox||4–2||5,714||
|-
! scope="row" style="text-align:center; background:#ffb;"|
|||New York Mets||San Diego Padres||2–1||3,640||
|-
!scope="row" style="text-align:center"|
|||Chicago Browns||Boston Reds||10–4||846||
|-
!scope="row" style="text-align:center"|
|||Providence Grays||Boston Beaneaters||2–1||505||
|-
! scope="row" style="text-align:center"|
|||Cleveland Indians||St. Louis Cardinals||2–0|| rowspan="14" |18||1,725||
|-
!scope="row" style="text-align:center"|
|||Milwaukee Brewers||Atlanta Braves||4–1||1,325||
|-
!scope="row" style="text-align:center"|
|||Toronto Blue Jays||Kansas City Royals||3–0||4,672||
|-
! scope="row" style="text-align:center; background:#ffb;"|
|||Seattle Mariners||Texas Rangers||bgcolor="#ffbbbb"|2–3||4,875||
|-
!scope="row" style="text-align:center"|
|||Los Angeles Dodgers||Atlanta Braves||6–0||1,427||
|-
!scope="row" style="text-align:center"|
|||Montreal Expos||Chicago Cubs||4–2||1,279||
|-
!scope="row" style="text-align:center"|
|||New York Yankees||California Angels||4–0||1,778||
|-
! scope="row" style="text-align:center; background:#ffb;"|
|||California Angels||Chicago White Sox||3–2||5,714||
|-
!scope="row" style="text-align:center"|
|||Houston Astros||Cincinnati Reds||6–1||1,283||
|-
! rowspan="2" scope="row" style="text-align:center; background:#ffb;" |
||| rowspan="2" |Los Angeles Dodgers||Chicago Cubs||10–2||2,396||
|-
|||San Francisco Giants||5–2||2,396||
|-
! scope="row" style="text-align:center; background:#ffb;"|
|||Cleveland Indians||Detroit Tigers||bgcolor="#ffbbbb"|1–4||2,581||
|-
!scope="row" style="text-align:center"|
|||Milwaukee Brewers||Boston Reds||bgcolor="#ffbbbb"|4–5||659||
|-
!scope="row" style="text-align:center"|
|||Boston Reds||St. Louis Maroons||bgcolor="#ffbbbb"|0–1||950||
|}
18 strikeouts in extra-inning games
thumb|upright|[[Nolan Ryan amassed 18 or more strikeouts in a nine-inning game twice, as well as 19 strikeouts in extra-inning games three times.|alt=A man in a white baseball jersey with "ASTROS" on the chest and orange and yellow stripes on his shoulders pitches a baseball with his right hand.]]
Eight different pitchers have struck out at least 18 batters in an extra-inning Major League Baseball (MLB) game to date. Only Nolan Ryan accomplished the feat more than once in his career and no player has ever struck out more than 21 batters in a game.
The following list is kept separate from the above list of pitchers who have struck out 18 or more batters in a nine-inning game. This is due to the differing number of innings pitched during an extra-inning game, the lack of a definitive endpoint to the game that would otherwise allow for a fair comparison to be made, and the advantage of having more opportunities to strike out players during an extra-inning game as opposed to one lasting nine innings.
{| class="wikitable"
|+Key
!scope="row"|IP
|Innings pitched by the pitcher in the game
|}
{| class="wikitable sortable plainrowheaders" style="text-align:center;"
|+MLB pitchers with 18 strikeouts in an extra-inning game
!scope="col"|Pitcher
!scope="col"|Date
!scope="col"|Team
!scope="col"|Opposing team
!scope="col"|Score
!scope="col"|Strikeouts
!scope="col" width="8%"|IP
!scope="col"|Career Ks
!scope="col" class="unsortable"|Refs
|-
!scope="row" style="text-align:center"|
|||Washington Senators||Baltimore Orioles||2–1||21||16||345||
|-
! scope="row" style="text-align:center; background:#ffb;"|
|||Arizona Diamondbacks||Cincinnati Reds||4–3||20||9