Interesting, when it comes to fastballs, there is a fundamental difference in analyzing whiffs depending on the reasonβ'under' or 'late'βso we have no choice but to look at them separately. That, of course, will lead to a SSS issue. Anyway, it's nice to see this research.
Using 2026 data so far: Velocity difference between fastball (just 4S and 2S) has the largest influence on average miss distance on an offspeed pitch w =2 strikes among several traits, but was still relatively inconclusive.