The Change: Strikeouts Minus Walks, But With Popups
We know that strikeout minus walk percentage is the best in-season predictor, or at least we knew that the last time someone checked. We know that pop-ups are automatic outs, and that they have the same season-to-season correlation (.49) as strikes thrown, or at least we know that if you define pop-ups as infield flies per ball in play (PU/BIP) instead of just IFFB (which is PU/FB). And that means we know that these three metrics are three of the strongest by year-to-year correlation, at least among the metrics that the pitcher has the most control over.
Since we ‘know’ these things about as well as you can know things in baseball, it seems about right to combine them into a simple metric. Strikeouts plus pop-ups (the good things) minus walks (the bad things). It’s a quick and easy way to rank pitchers based on what they actually did last year, and it’s how I’ll sort my rankings the very first time I start working on them.