In baseball statistics, strikeouts per nine innings pitched (K/9, SO/9, or SO/9IP) is the mean of strikeouts (or Ks) by a pitcher per nine

innings pitched In baseball, innings pitched (IP) are the number of innings a pitcher has completed, measured by the number of batters and baserunners that are put out while the pitcher is on the pitching mound in a game. Three outs made is equal to one innin ...

. It is determined by multiplying the number of strikeouts by nine, and dividing by the number of innings pitched. To qualify, a pitcher must have pitched 1,000 innings, which generally limits the list to starters. A separate list is maintained for

reliever In baseball and softball, a relief pitcher or reliever is a pitcher who enters the game after the starting pitcher is removed because of fatigue, ineffectiveness, injury, or ejection, or for other strategic reasons, such as inclement weather d ...

s with 300 innings pitched or 200 appearances.

Leaders

The all-time leader in this statistic through 2021 was

Robbie Ray Robert Glenn Ray (born October 1, 1991) is an American professional baseball pitcher for the Seattle Mariners of Major League Baseball (MLB). He previously played for the Detroit Tigers, Arizona Diamondbacks, and Toronto Blue Jays. Ray was an ML ...

(11.10). The only other pitchers who had averaged over 10 strikeouts were Chris Sale (11.08), Yu Darvish (11.04),

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. Prior to playing professionally, deGrom attend ...

(10.88), Max Scherzer (10.73), Randy Johnson (10.61), Stephen Strasburg (10.55), Gerrit Cole (10.39),

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 rooki ...

(10.32),

Aaron Nola Aaron Michael Nola (born June 4, 1993) is an American professional baseball pitcher for the Philadelphia Phillies of Major League Baseball (MLB). Nola was born in Baton Rouge, Louisiana, and played baseball alongside his older brother Austin. H ...

(10.08), 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 in 2022 were Carlos Rodon (11.98), Shohei Ohtani (11.87), and Gerrit Cole (11.53). Among qualifying relievers,

Aroldis Chapman Albertín Aroldis Chapman de la Cruz (; born February 28, 1988) is a Cuban-born American professional baseball relief pitcher who is a free agent. He has played in Major League Baseball (MLB) for the Cincinnati Reds, New York Yankees and Chica ...

(14.88) was the all-time leader in strikeouts per nine innings through 2020, followed by Craig Kimbrel (14.66), Kenley Jansen (13.25), Rob Dibble (12.17), David Robertson (11.93), and Billy Wagner (11.92).

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 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