Should Blake Snell have been pulled in the 2020 World Series? I created a Degradation Index for pitcher fatigue to determine whether this was the right choice.
Ever since Kevin Cash took out Blake Snell because his velo dropped in the 2020 World Series I wanted to find a better way to determine when to pull a pitcher.
To solve this, I created a Degradation Index to quantify pitcher fatigue. This index is based on variance in arm angle and extension, and achieves a much higher specificity than standard velo drops. By tracking pitcher fatigue in mechanics, teams can save their bullpens only for when it is most important.
I used an XGBoost regressor to filter out pitcher's intentional changes in mechanics so that the isolation forest algorithm only checks the residuals for fatigue-caused anomalies.
I just published a comprehensive breakdown on Medium, and the code is open on GitHub. Any and all feedback is very appreciated.