In baseball statistics, strikeouts per nine innings pitched (abbreviated 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.
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The all-time Major League Baseball (MLB) career leader (minimum of 1,000 innings pitched) in this statistic through 2022 is Chris Sale (11.06). The only other pitchers who had averaged over 10 K/9 are: Robbie Ray (11.03), Jacob deGrom (10.96), Yu Darvish (10.70), Max Scherzer (10.69), Randy Johnson (10.61), Stephen Strasburg (10.55), Gerrit Cole (10.45), Kerry Wood (10.32), Pedro Martinez (10.04) and Aaron Nola (10.02).[1]
The top three during the 2022 season were Carlos Rodon (11.98), Shohei Ohtani (11.87), and Gerrit Cole (11.53).[2]
The career leader in K/9 among MLB relievers (minimum of either 300 innings pitched or 200 appearances) through 2020 was Aroldis Chapman (14.88), followed by Craig Kimbrel (14.66), Kenley Jansen (13.25), Rob Dibble (12.17), David Robertson (11.93), and Billy Wagner (11.92).[3][4][5]
In 2022, Kyle Harrison led Minor 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]
Un efecto de K/9 es que puede recompensar o "inflar" los números de los lanzadores con altos promedios de bateo de bolas en juego (BABIP). Dos lanzadores pueden tener las mismas tasas de K/9 a pesar de ponchar a un porcentaje diferente de bateadores, ya que un lanzador lanzará a más bateadores para obtener el mismo número acumulativo de ponches. Por ejemplo, un lanzador que poncha a un bateador en una entrada, pero también concede una base por bolas o un hit , poncha a un porcentaje menor de bateadores que un lanzador que poncha a un bateador en una entrada sin permitir un corredor, pero ambos tienen el mismo K/9. [8]