We know, not only because of Taylor Jungmann, but also from the Brewers’ starter, that not all pitches thrown seldomly with good results will remain as successful when thrown more often. Sometimes pitches are successful because they are rare and unexpected. Any batter can hit an eephus if you tell them it’s coming, but your average eephus gets 7% swinging strikes, mostly because they are surprising.
That said, we have some research on what makes curves and changeups good in terms of movement. So if we combine a pitch with elite results in a small sample with an appraisal of how good the movement and velocity on the pitch, we should be able to say with some confidence that the pitch is good.
In order to find our subjects, I merely set the filter low for pitch types (40 pitches) and looked for starters with elite results on changeups, curves, and sliders. It takes 150 plate appearances for strikeout rate to be stable, so this is probably a small sample even for pitch type ‘strikeout rate’, but we’re scouting here, trying to find the elite before they are actually elite.