Jeff Zimmerman of RotoGraphs and other outlets turned me on to a new baseball rule recently: The Yu Darvish Rule. As seen in the tweet below, unless your name is Yu Darvish, you should not be throwing more than four pitches.
Yu Darvish Rule Violation— Jeff Zimmerman (@jeffwzimmerman) April 26, 2022
Aaron Civale with seven pitches thrown at least 5% of the time.
Five of them have not generated a single swing-and-miss. pic.twitter.com/6EQz6jp2Dt
The specific violator being highlighted here is Aaron Civale, who has thrown six different pitches this year, each more than 9% of the time. Rather than keeping hitters guessing, however, this has resulted in an ERA of 9.58, FIP of 5.48, and -0.1 fWAR (small sample size applies, as this is only through 10.1 innings). Moreover, batters are making solid contact and barreling the ball (11.1 and 13.9%, respectively) at greater rates than ever before in Civale’s career.
None of Civale’s six pitches (cutter, curve, four-seam, sinker, slider, splitter) have been particularly good by FanGraphs’ Pitch Info pitch values. In fact, the only offering above average in the weighted per 100 pitches value is the cutter, which has a value of 2.11; the rest of Civale’s pitches are below average, with the splitter and sinker valued especially poorly at -4.02 and -5.69, respectively.
This is borne out in Baseball Savant’s stats as well, with the cutter generating whiffs 32.1% of the time and being a put-away pitch 25% of the time. The sinker, on the other hand, has the highest xwOBA, .496, has an average exit velocity of 98.4 mph, and has generated zero whiffs.
This is in keeping with previous seasons, like 2021 and 2020, when the sinker was also Civale’s worst offering by xwOBA and exit velocity. It’s a clear case of needing to simplify, which the Yu Darvish Rule flowchart makes abundantly and bluntly clear.
Just across the dugout on any given night is an example of this working in practice. Though he was never a Darvish Rule violator, Triston McKenzie has simplified his approach and found more consistent results since his debut.
In 2020, McKenzie came to the big leagues with four offerings: four-seam, slider, curve, changeup. His least frequently thrown offering was the change, but he still delivered it to batters 10% of the time. Batters appreciated that 10% to the tune of a .452 wOBA (.457 xwOBA) and 88.5 mph exit velocity, which translated to 12 barrels (or 1 barrel for every 5 changeups thrown). McKenzie learned his lesson somewhat for 2021 and decreased his usage of the change to just 1.3% of his offerings, but opponents still teed off on the pitch with an .825 wOBA (.427 xwOBA) and 101.6 mph exit velocity (3 barrels; 1 for every 8 changeups thrown). FanGraphs’ Pitch Info Pitch Values gave it a value of -4.22 and -9.02 for 2020 and ‘21, respectively.
In the brief 2022 season, McKenzie has thrown exactly zero changeups. His cost-benefit analysis has rendered the pitch obsolete. This decision has his ERA at 3.71, FIP at 3.24, and HR/FB at 5.6% — all new or near career bests. The change has let his four-seamer play up, generating more whiffs, and helped the curveball (now his biggest change of pace) immensely. In 2020, the curve was a put-away pitch 17.9% of the time, whereas it is a put-away pitch 27.3% of the time in 2022 and also generated the most whiffs (28.6%).
McKenzie still has room for growth as a pitcher, specifically in differentiating the curve and slider, as they have drifted closer together in horizontal movement. But his ability to change his arsenal is a lesson that Civale could stand to learn from, and could bend the arc of the trend lines below in the right direction.