Inbaseball statistics,strikeouts per nine innings pitched (abbreviatedK/9,SO/9, orSO/9IP) is themean ofstrikeouts (orKs) by apitcher per nineinnings pitched. It is determined by multiplying the number of strikeouts by nine, and dividing by the number of innings pitched.
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The all-timeMajor League Baseball (MLB) career leader (minimum of 1,000innings pitched) in this statistic through 2024 isBlake Snell (11.23). The only other pitchers who had averaged over 10 K/9 are:Chris Sale (11.09),Robbie Ray (11.07),Jacob deGrom (10.97),Max Scherzer (10.65),Randy Johnson (10.61),Yu Darvish (10.59),Stephen Strasburg (10.55),Gerrit Cole (10.37),Kerry Wood (10.32), andPedro Martinez (10.04).[1]
The top three during the2024 season were Chris Sale (11.40),Sonny Gray (10.98), andCole Ragans (10.77).[2]
The career leader in K/9 among MLB relievers (minimum of either 300 innings pitched or 200 appearances) through 2020 wasAroldis Chapman (14.88), followed byCraig Kimbrel (14.66),Kenley Jansen (13.25),Rob Dibble (12.17),David Robertson (11.93), andBilly Wagner (11.92).[3][4][5]
In 2022,Kyle Harrison ledMinor League Baseball 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.[6][7]
One effect of K/9 is that it may reward or "inflate" the numbers for pitchers with highbatting 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 awalk or ahit, 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.[8]