[Skipaway]

I know there are studies showing the longer the delay between pitches, the less likely are hitters going to be fooled by speed changes. So apparently there should be more factors than just the speed differences and pitch types. And some pitchers just have different approaches in different situations, which would be yet another factor.

I think the problem would be the disconnect between the known factors and the statistical outcomes. Even if the pitch type effects are modeled perfectly, there will still need some kind of generic cover-it-all rating to represent whatever still unknown.