Strikeouts per 9 innings pitched

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In baseball statistics, strikeouts per 9 innings pitched (K/9, SO/9, or SO/9IP) is the mean of strikeouts (or Ks) by a pitcher per nine innings pitched. 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 1000 innings, which generally limits the list to starters. A separate list is maintained for relievers with 300 innings pitched or 200 appearances.

The all-time leader in this statistic is Chirs Sale (10.84). The only other players who have averaged over 10 (as of 8/20/2018) are Randy Johnson(10.61),Stephen Strasburg (10.55), Kerry Wood (10.32), Max Scherzer (10.35). and Pedro Martínez (10.04).[1]

Among qualifying relievers, Rob Dibble (12.17) is the all-time leader in strikeouts per nine innings.[2][3][4] Active leader David Robertson (12.03),[5] Craig Kimbrel (14.7) [6] and Aroldis Chapman (15.3) [7] are the only other qualifying relievers averaging more than 12.

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. [8]


  1. ^ "K/9IP All Time Leaders". 
  2. ^ "K/9IP leaders, minimum 200 appearances". 
  3. ^ "K/9IP leaders, minimum 300 innings pitched". 
  4. ^ "Rob Dibble Statistics". 
  5. ^ "David Robertson Statistics". 
  6. ^ Craig Kimbrel Stats |
  7. ^ Aroldis Chapman Stats |
  8. ^ James Gentile (October 8, 2012). "Stop using K/9 and BB/9!". Beyond the Box Score. 

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