Earlier this week, Ben Clemens from Fangraphs wrote an interesting piece highlighting the velocity differential between Kevin Gausman's four-seam fastball in two-strike counts versus in all other counts. In the piece, Clemens poses an interesting question about how this velocity boost impacts performance in these counts. The uptick has been a trend throughout Gausman's career, yet year-to-year results have shown different outcomes as reflected in the pitch's RV/100. While Clemens focuses on other matters in his post, and a follow-up post later in the week, I found this performance fluctuation to be particularly interesting and was interested in exploring what, if any, trends might exist in helping us understand what factors contribute in determining whether Gausman's fastball is successful in two-strike counts within a given year.

Looking at Fangraphs' PitchingBot and Stuff+ models, the pitch doesn't appear to have any significant increases or decreases in its grade across each of his previous 3 seasons.

• 2021
  • PitchingBot: 49
  • Stuff+: 105
• 2022
  • PitchingBot: 52
  • Stuff+: 111
• 2023
  • PitchingBot: 52
  • Stuff+: 110

When breaking down a pitch's performance, it can be useful to assess performance for right-handed and left-handed hitters separately. Often a pitcher's approach with a specific pitch type will be different for the two, and depending on the pitch's qualities, can play either better or worse for one side versus the other. When splitting RV/100 by batter handedness and season, we see improvements into positive value territory for both sides between the 2021-2022 and 2023 season, as reflected in the overall numbers as well, but even more interesting might be the larger fluctuations in performance versus right-handed hitters.

So while some signal for improvement in performance versus lefties exists, we're seeing the pitch's performance versus right-handed hitters hold more weight in determining the overall RV/100 figures we saw in Ben Clemens' original post. In Gausman's below-average seasons (2021-2022), performance versus rights is more dramatically below-average, and in his above-average season (2023), he is more dramatically above-average versus righties in comparison to performance versus lefties.

What might be driving this leap in 2K FB performance between 2022 to 2023? Looking at performance splits versus right-handed hitters, nothing stands out from a hitter tendency perspective. Swing% and Chase% didn't change much between the two seasons, however as we would expect given the run value differences, we see much worse hitter performance including an uptick in swing-and-miss, as well as contact quality metrics like Hard-Hit% and xwOBAcon.

Gausman's performance improvement without any apparent change in hitter tendencies or stuff quality leads me to wonder if he was pitching to more effective locations against righties in 2023.

It seems that Gausman shifted his locations further down in the zone in 2023, increasing the proportion of his pitches to the middle and lower thirds of the zone vertically in a tradeoff with a lower proportion of pitches to the upper third. 

How intentional was this change? Did Gausman recognize an opportunity for his fastball to perform better low in the zone in these situations? Looking at similar performance metrics used above split by vertical zone location with just three location buckets...

Prior year performance likely wouldn't have given Gausman any reason for making pitching low a higher priority in 2023. However, I wonder if getting particularly roughed up on the upper third of the zone in 2022 made him second guess those locations going into 2023.

It's entirely possible that specific fastball locations weren't much of a consideration for Gausman in any of these seasons. I could see these differences being left mostly to random variation (especially in smaller samples), with most of his focus being on gaining the couple ticks in velocity like Clemens highlighted. It is possible that the desire to throw harder in two-strike counts makes it more difficult to locate in specific areas and the locations took a backseat to velocity, resulting in Gausman spraying to different areas of the zone.