K/9 (Strikeouts per 9 Innings)
K/9 scales a pitcher’s strikeouts to a standard nine innings, which makes a reliever and a starter comparable on the same axis.
Its weakness is the denominator. A pitcher who allows a lot of baserunners faces more batters per inning and can post a strong K/9 without actually missing bats at an elite rate. K% — strikeouts divided by batters faced — corrects for that and is the sharper of the two.
For NUT the raw strikeout count is what feeds FIP, because a strikeout only prevents a run if it actually happened. K/9 is the better tool for asking how hard a pitcher is to hit; NUT answers how much he produced.
What is a good K/9?
K/9 is the rate version of the biggest positive input to pitching NUT. It is useful for comparison, but NUT uses the raw counts so that innings still matter.
How NUT Score works →