Are Walker Buehler’s Run Suppression Gains for Real?

Walker Buehler has been on a tear in the second half, leading all pitchers in WAR since the All-Star break at 1.8, just a hair ahead of Adam Wainwright, Frankie Montas, and Max Fried. For the season, he now ranks fourth in WAR among qualified starters (fifth if you include Jacob deGrom’s 92 preposterous innings), toting a 26.9% strikeout rate and a park-adjusted ERA 47% better than league average. His 2.11 ERA is more than half a run better than any other season in his career, and the park adjusted figure is his best by 15 points. It’s another great season from one of the consistently best pitchers in the majors; since becoming a full-time starter for the Dodgers back in 2018, Buehler has posted the 11th-most pitching WAR with the 19th-most innings pitched.

I am not breaking any news by pointing out that Buehler has been and continues to be excellent. The surface-level numbers indicate he has never been better. What caught my eye, however, was how he has gone about doing that. There have been some noticeable changes under the hood. For example, at age 26, he has lost over a full tick of velocity on his fastball compared to any prior season; based on my own research, you would expect a player of his age to lose only about 0.15 mph.

Buehler has also lost almost two percentage points on his strikeout rate. On its face, missing less bats and losing velocity is never something you want to see in a pitcher. (That said, he has brought his ground-ball rate back to pre-2020 levels, going from 35.5% last season to 43.8% this year, similar to his ’19 rate as well as a tick above the rest of the league in 2021.)

It is fair to wonder if Buehler has taken a small step back despite his stellar results, as players that lose velocity year over year generally also lose effectiveness in terms of run suppression and strikeouts. I took every season in the pitch tracking era for starting pitchers who threw at least 100 innings, then paired the seasons (each season had to have 100 innings pitched), took the changes in velocity, ERA, FIP, and strikeout rate, and charted them. Here’s where Buehler falls in terms of his velocity decrease:

Buehler’s velocity change falls on the wrong end of all three curves. These curves describe the starting pitching population in general, however, so he could be attacking hitters differently to compensate for his velocity dip. Looking at thousands of pitchers is not exactly conducive to potential edge cases.

This is not to say he is not among the league’s elite; he most definitely is. What I wanted to figure out is if Buehler is being propped up by some batted ball luck or if he has changed his approach at the expense of strikeouts. To that end, he has made some tweaks to his pitch mix, possibly in response to the lack of velocity, and is leaning more on his slider and cutter, as well as incorporating a changeup (mostly to lefties), at the expense of his four-seamer.

This change makes sense; his fastball has not been as effective an offering as it has been in the past.

The swinging-strike rate on Buehler’s fastball has steadily decreased over time, hitting a nadir in 2021, even with more swings (as a percentage of pitches) and more chases than last season. The curveball has also seen a noticeable decline in performance across the board, and I wonder if this is a result of using his fastball less often and to lesser effect, as the curve tunnels off of it. The real boons to his arsenal have been the slider and changeup, the latter of which he did not use at all in 2020 but has gotten swinging strikes out of almost 33% more than average. The slider, meanwhile, has been especially potent in inducing chases.

Buehler is also varying the locations at which he throws each of his pitches. His zone rate is down a fraction of a percentage point from 2020, and his chase rate has increased by 1.5%, a promising trend. He has also yielded strikes on the first pitch 65.7% of the time, going from slightly below-average last year to firmly above the league mean. Using the Gameday zones defined by MLBAM (which you can find in the Baseball Savant search tool), you can see Buehler is throwing a higher percentage of his pitches up in the zone (zones one, two and three), mostly with his four-seamers (a 5.7 percentage point increase year over year) and cutters (10.6 percentage points), and has thrown more pitches down and off the plate, mostly with his slider.

One thing that cannot be ignored and that is likely behind both using the four-seamer less and the pitch’s precipitous fall in whiff rate is a change in spin rate following enforcement of the sticky substance ban. Spin rate is partially a product of velocity, so Buehler’s decrease in that stat this season should not come as a surprise. But even when you account for this relationship (by dividing spin rate by velocity, which I will refer to as spin-velocity ratio, or SVR), the change is still visible.

You can see a sharp decline in SVR right after reports emerged that the enforcement of sticky substances would begin in earnest on June 3:

That date is marked with the red dashed line; both the ranges and averages by start began to fall after that point.

What is most surprising is that Buehler seems to have improved despite this. After a brief dip around the date where the enforcement was reported, his strikeout rate has steadily climbed as the season has gone on:

Buehler’s adjustment to his repertoire post-June 3 is even more stark than the year-over-year changes, as he has accelerated his use of his breaking pitches and changeup:

The same holds true when split by handedness, where he has relied on his changeup more against lefties (6.3% versus lefties versus one lone changeup to righties) and increased his usage with the slider against right-handers to roughly 35%.

Buehler has improved as the season has gone along, even in the face of his spin rate degradation, and while losing velocity is never a positive development, he has compensated with increased use of his excellent breaking pitches as well as the return of his changeup. He’s also been aided by a .239 BABIP and a 9.9% HR/FB rate, compared to a 13.0% mark pre-2021. That mostly explains the 1.02 gap between his ERA and FIP, the largest among qualified starters this season. Some of this batted ball fortune should be attributed to Buehler, though; he has allowed below-average figures in terms of both barrel rate and hard-hit rate, as well as a .340 wOBAcon versus a .370 rate for the rest of the league.

That .239 BABIP is a bit low even for a pitcher displaying great command, as is the home-run rate, which is about a third lower than the major league average. But Buehler has been locating in such a way that we should expect his results on contact against to at least be a little below average. Pair that with a great strikeout rate, and you have one of the best pitchers in the league. Is he a 2.11 ERA pitcher? Probably not, but he has shown the ability to adjust. That will be essential if the Dodgers hope to avoid the dreaded wild-card game, win the NL West, and defend their title.