It’s well understood that a repeatable delivery helps a pitcher. It may contribute to deception by disguising pitches longer as well as arm health and longevity by avoiding new and unexpected stress on the arm. In modern baseball parlance, “tunneling” is as widespread and desired an attribute as any other, and one look at a PitchingNinja overlay makes it clear why. Elite pitchers excel at repeating their release point and the first few feet of ball flight, and new tools like Driveline Edge allow for measurement and testing in pitch design for all players. While there’s little debate about the benefits of consistency, considerably less has been done in regards to the precise pitch result and swing outcome effects of greater release repeatability and “tunneling.” Knowing more about the expected improvement in outcome from a change in a pitcher’s release pattern gives us a better guide to contextualizing release point data across outings and see how it translates to in-game performance. In trying to develop a useful comparison, the outcome reference point I first settled on was swing rate -- with the intuition being that the better a pitcher “tunnels,” and the more consistent they are at release, the higher the swing rate on their primary offspeed pitch would be. Using data from the 2020 season, my initial results did not conform to that hypothesis. Charting swing rate against the pythagorean difference in release point compared to each pitcher’s fastball {Sqrt[(HeightFastball - HeightOffspeed)2 + (Horiz. PositionFastball - Horiz. PositionOffspeed)2]} returned a surprisingly inconclusive result. There was no compelling relationship visible in the data, and tests of the bivariate pearson correlations confirmed this, with Sliders having r = .079 and Curveballs coming in at just r = .110. This seemingly flew in the face of the conventional wisdom, and the relationships were no stronger when testing against swing and miss or chase rate alternatively. The anecdotal and experiential evidence in favor of a more repeatable release having an appreciable positive relationship with swing outcomes is strong enough that it warranted further investigation, and resolving deviation from average Fastball release position into its vertical and horizontal components significantly changed the tests’ results. Once release height and horizontal position (“Release Side” per Trackman) were isolated and tested independently the data began to confirm my suppositions and general intuition. Starting with Sliders, splitting height and side revealed that release side has little appreciable effect but release height does have the expected relationship with swing rate. Compared to the combined r value of just .079, release height returned r = -.295 with swing rate. Applying the same process to Curveballs produced an even more impressive outcome: The plot shows an even stronger swing rate dependence on release height, with r = -.327 compared to a relatively inconclusive positive relationship with release side. This exaggeration in result for Curveballs was not surprising, given their relative ease of identification compared to most sliders. The tendency of a curveball to “pop” up out of the pitcher’s hand aggravates the effects of a difference in release point and trajectory, placing a greater emphasis on releasing a curveball at the same height as a pitchers’ fastball. Having a different release point as well as a different look out of hand predictably fails to fool a hitter, minimizing the effectiveness of the Curveball. That said, those unique Curveball release characteristics can have other benefits for a pitcher, particularly so in regards to producing looking strikes. The benefits of release consistency seem to be turned on their head when looking at strikes taken, with height and side deviations contributing to more looking strikes: This is certainly something to keep in mind for pitch design, as a sufficiently different “look” to an offspeed pitch may surprise or freeze a hitter and steal some strikes. In assembling an arsenal, it may be beneficial to have the best of both with a well-disguised Slider and a change-of-pace Curveball as weapons.
All that said, both the data and statistical relationships were fairly constrained, leaving wide confidence intervals and necessitating some deeper analysis. I would expect the relationships between pitch consistency and swing outcomes to be strengthened by looking at the first few feet of flight rather than just release, allowing for elite “tunnelers” to separate themselves from the pack and produce a more convincing statistical result. Moving forward, it appears that release height is king when it comes to deception, allowing some wiggle room in horizontal release position to accommodate a player’s habits and feel. Despite the temptation to do so, it may not be beneficial to try and eliminate a pitcher’s tendency to change slot or arm angle on their offspeed pitches as long as height is well matched to their fastball.
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