How is 'Stuff' Calculated?

​Overview
The "Stuff" rating on Pitcher cards is not used by the game engine. It is provided for informational purposes, condensing the pitcher’s overall effectiveness to two single-digit numbers (one versus lefty batters and one versus right batters).

The average Stuff rating is 1 point higher against same-handed batters than against opposite-handed batters. Gaps larger than 1 show a large "platoon advantage" — a trait indicative of a pitcher that can be used as specialists against same-handed batters.

One point of Stuff also equates (roughly) to one level of Fatigue. For example, the Pedro Martinez card above shows a Stuff of 8 versus lefties. With 3 levels of Fatigue, he is roughly as effective as a pitcher with a Stuff of 5.

Calculation
​Stuff estimates a pitcher's overall effectiveness (versus lefties and righties, respectively) by calculating the number of runs allowed or prevented on their Pitching Table, compared to the league average, using the following linear weights:

• HR allowed = 1.65 runs
• non-HR hits = 0.78 runs
• BB = 0.55 runs
• K = -0.06 runs

I use these numbers to calculate runs allowed per 44 batters faced. Then I scale the league average up to 5.0 and invert the ratings so that higher values represent fewer runs allowed per 44 batters faced. I use 44 because it means that 1 point of stuff roughly equals 1 WAR per 100 innings pitched. And 1 point of stuff roughly offsets the negative effect of 1 point of Fatigue.