baseball statistics Baseball statistics include a variety of metrics used to evaluate player and team performance in the sport of baseball. Because the flow of a baseball game has natural breaks to it, and player activity is characteristically distinguishable ind ...

, strikeouts per nine innings pitched (abbreviated K/9, SO/9, or SO/9IP) is the

mean A mean is a quantity representing the "center" of a collection of numbers and is intermediate to the extreme values of the set of numbers. There are several kinds of means (or "measures of central tendency") in mathematics, especially in statist ...

strikeouts In baseball or softball, a strikeout (or strike-out) occurs when a batter accumulates three strikes during a time at bat. It means the batter is out, unless the third strike is not caught by the catcher and the batter reaches first base safe ...

(or Ks) by a

pitcher In baseball, the pitcher is the player who throws ("Pitch (baseball), pitches") the Baseball (ball), baseball from the pitcher's mound toward the catcher to begin each play, with the goal of out (baseball), retiring a batter (baseball), batter, ...

per nine

innings pitched In baseball, the statistic innings pitched (IP) is the number of innings a pitcher has completed, measured by the number of Batter (baseball), batters and baserunners that have been put out while the pitcher is on the Baseball field#Pitcher's mou ...

. It is determined by multiplying the number of strikeouts by nine, and dividing by the number of innings pitched.

Leaders in Major League Baseball

The all-time

Major League Baseball Major League Baseball (MLB) is a professional baseball league composed of 30 teams, divided equally between the National League (baseball), National League (NL) and the American League (AL), with 29 in the United States and 1 in Canada. MLB i ...

(MLB) career leader (minimum of 1,000

) in this statistic through 2024 is

Blake Snell Blake Ashton Snell (born December 4, 1992) is an American professional baseball pitcher for the Los Angeles Dodgers of Major League Baseball (MLB). He has previously played in MLB for the Tampa Bay Rays, San Diego Padres, and San Francisco Giants ...

(11.23). The only other pitchers who had averaged over 10 K/9 are:

Chris Sale Christopher Allen Sale (born March 30, 1989) is an American professional baseball pitcher for the Atlanta Braves of Major League Baseball (MLB). He has previously played in MLB for the Chicago White Sox and Boston Red Sox. He throws left-handed ...

(11.09), Robbie Ray (11.07),

Jacob deGrom Jacob Anthony deGrom (born June 19, 1988) is an American professional baseball pitcher for the Texas Rangers of Major League Baseball (MLB). He has previously played in MLB for the New York Mets. DeGrom began playing baseball as a shortstop ...

(10.97),

Max Scherzer Maxwell Martin Scherzer (born July 27, 1984), nicknamed "Mad Max", is an American professional baseball pitcher for the Toronto Blue Jays of Major League Baseball (MLB). He has previously played in MLB for the Arizona Diamondbacks, Detroit Tige ...

(10.65),

Randy Johnson Randall David Johnson (born September 10, 1963), nicknamed, "the Big Unit," is an American former professional baseball pitcher who played 22 seasons in Major League Baseball (1988–2009) for six teams, primarily the Seattle Mariners and Arizo ...

(10.61),

Yu Darvish , more commonly known as Yu Darvish (ダルビッシュ有), is a Japanese professional baseball pitcher for the San Diego Padres of Major League Baseball (MLB). He has previously played in MLB for the Texas Rangers (baseball), Texas Rangers, Lo ...

(10.59),

Stephen Strasburg Stephen James Strasburg (; born July 20, 1988) is an American former professional baseball pitcher who spent his entire 13-year Major League Baseball (MLB) career with the Washington Nationals. He is a three-time Major League Baseball All-Star G ...

(10.55),

Gerrit Cole Gerrit Alan Cole (born September 8, 1990) is an American professional baseball pitcher for the New York Yankees of Major League Baseball (MLB). He has previously played in MLB for the Pittsburgh Pirates and Houston Astros. Cole played for the bas ...

(10.37),

Kerry Wood Kerry Lee Wood (born June 16, 1977) is an American former baseball pitcher who played 14 seasons in Major League Baseball (MLB) for the Chicago Cubs, Cleveland Indians, and New York Yankees. Wood first came to prominence as a 20-year-old rookie, ...

(10.32), and

Pedro Martinez Pedro is a masculine given name. Pedro is the Spanish, Portuguese, and Galician name for ''Peter''. Its French equivalent is Pierre while its English and Germanic form is Peter. The counterpart patronymic surname of the name Pedro, meaning ...

(10.04). The top three during the season were Chris Sale (11.40), Sonny Gray (10.98), and Cole Ragans (10.77). The career leader in K/9 among MLB relievers (minimum of either 300 innings pitched or 200 appearances) through 2020 was

Aroldis Chapman Albertín Aroldis Chapman de la Cruz (; born February 28, 1988) is a Cuban-born American professional baseball relief pitcher for the Boston Red Sox of Major League Baseball (MLB). He has previously played in MLB for the Cincinnati Reds, New Y ...

(14.88), followed by

Craig Kimbrel Craig Michael Kimbrel (born May 28, 1988) is an American professional baseball pitcher in the Texas Rangers organization. He has previously played in Major League Baseball (MLB) for the Atlanta Braves, San Diego Padres, Boston Red Sox, Chicago ...

(14.66),

Kenley Jansen Kenley Geronimo Jansen (born September 30, 1987) is a Curaçaoan professional baseball pitcher for the Los Angeles Angels of Major League Baseball (MLB). He has previously played in MLB for the Los Angeles Dodgers, Atlanta Braves, and Boston Red ...

(13.25),

Rob Dibble Robert Keith Dibble (born January 24, 1964) is an American former Major League Baseball (MLB) pitcher and television analyst. Between 1988 and 1995, Dibble played for the Cincinnati Reds, Chicago White Sox and Milwaukee Brewers. He was a two-time ...

(12.17), David Robertson (11.93), and

Billy Wagner William Edward Wagner (born July 25, 1971), nicknamed "Billy the Kid", is an American former professional baseball pitcher who played 16 seasons in Major League Baseball (MLB) for the Houston Astros, Philadelphia Phillies, New York Mets, Boston ...

(11.92). In 2022, Kyle Harrison led

Minor League Baseball Minor League Baseball (MiLB) is a professional baseball organization below Major League Baseball (MLB), constituted of teams affiliated with MLB clubs. It was founded on September 5, 1901, in response to the growing dominance of the National Le ...

with 14.8 strikeouts per 9 innings, the highest rate for a pitcher in the minor leagues in a season (minimum of 100 innings pitched) dating back to 1960.

Analysis

One effect of K/9 is that it may reward or "inflate" the numbers for pitchers with high batting averages on balls in play (BABIP). Two pitchers may have the same K/9 rates despite striking out a different percentage of batters since one pitcher will pitch to more batters to obtain the same cumulative number of strikeouts. For example, a pitcher who strikes out one batter in an inning, but also gives up a

walk Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined as an "inverted pendulum" gait in which the body vaults over ...

or a hit, strikes out a lower percentage of batters than a pitcher who strikes out one batter in an inning without allowing a baserunner, but both have the same K/9.

References

Pitching statistics {{Baseball-stub