Addition by Subtraction: Fixing Dylan Bundy Long-Term

Some good pitchers, despite being good pitchers, throw bad pitches. And there are bad pitchers, too, who throw good pitches. Both are true, and one could make an argument a Venn Diagram of the two groups may overlap significantly, and that overlapping area is the group of pitchers toeing the line between breaking out and being unusable for fantasy purposes.

It stands to reason, then, that good and bad pitchers could benefit from easing off or completely abandoning their bad pitches. It’s one thing to evaluate a pitch based on its underlying metrics — its swinging strike rate (SwStr%), its ground ball rate (GB%), its velocity, and so on. It’s another thing to evaluate the pitch objectively by looking at its weighted on-base average (wOBA) allowed, which, I hope, in an adequately large sample, can indicate a pitch’s quality regardless of its peripherals. In theory, the larger the sample size, the greater the probability a pitch’s outcomes will converge with its inputs, such that the caveat “regardless of its peripherals” doesn’t actually mean anything. Given enough pitches thrown, the aforementioned underlying metrics will adequately inform the wOBA allowed.

Using PITCHf/x data from the last two years, I looked for (1) good pitchers who throws pitches that allow (2a) extremely bad wOBAs with (2b) unusually low BABIPs. Incurring high wOBAs on low BABIPs is less than ideal; if BABIP is subject to high variance and generally converges on the league average, then a bad pitch being “lucky” by BABIP suggests things will only get worse.

This post was going to be about several pitchers, each with their own problematic pitches, but I became too passionate about this single case. This is about Dylan Bundy, his abhorrently bad four-seamer, his fantastic slider, and how much his pitch selection is suffocating his potential. Ultimately, it’s about adding by subtracting.

To be clear, Bundy is not actually broken. Everyone has bad days at the office — it’s just that his was extraordinarily bad especially in light of how effective he had been for five weeks prior. In fact, I wrote about Bundy’s success just a couple of weeks ago, but it was prior to the Royals taking him behind the woodshed in one of Major League Baseball’s worst starts ever. The timing is serendipitous: three of the four home runs Bundy allowed came off his four-seamer. We’ve reached a breaking point.

Bundy’s four-seamer sucks. Among pitches thrown at least 2,000 times (by good or near-good pitchers) since the start of the 2016 season, his fastball might be the worst (or maybe 2nd-worst, behind only Chris Archer’s four-seamer). It allowed a 136 wRC+, roughly, during that span. Take your pick: for two years, on more than half his total pitches thrown, Bundy’s four-seamer turned his opposition into Charlie Blackmon, Justin Turner, Carlos Correa, Jose Ramirez, Edwin Encarnacion, et al. Thrown 2,540 times since the start of 2016, it’s equivalent to 25-plus starts’ worth of fastballs thrown to lineups comprised entirely of elite hitters. It’s hard to imagine a positive full-season outcome that has such a vulnerable half-season embedded in it.

Credit where it’s due: Bundy’s fastball usage is trending in the right direction this season, although he still hasn’t taken the correction far enough. Meanwhile, the slider he introduced last year, which I’ve mentioned before, allowed an anemic 40 wRC+ in 2017 thanks to one of the most lethal single-pitch whiff rates in baseball (25.2%). Few pitchers can boast about throwing one of baseball’s best pitches as well as one of baseball’s worst.

At first glance, it seems the slider has only grown more effective, incurring a 33.7% whiff rate. It’ll likely regress — a 175-pitch sample is not large enough to conclude conclusively the signal is anything but noise — but a pitch that allows a 22(!!!) wRC+ across eight starts cannot be ignored. Yet Bundy still throws it only one-fourth of the time. He needs to tip the scales in favor of his slider. As aforementioned, his reliance upon his four-seamer is dwindling, but only because he reintroduced his sinker (YO, EVERYONE: PLEASE STOP THROWING SINKERS), not because he’s throwing his slider more.

It’s hard to anticipate any scenario in which Bundy gets worse by featuring his slider more prominently. Patrick Corbin ramped up his electric slider usage from 33% in April 2017 to 43% in September 2017. It’s no surprise he dominated the second half of 2017 (3.26 ERA in 88.1 innings post-All-Star Break) and carried that success into what has been, to date, a full-blown breakout. Bundy’s slider, believe it or not, was better than Corbin’s prior to this season. So far this year, Bundy’s slider barely trails Corbin’s in terms of effectiveness (22 wRC+ and 6 wRC+, respectively), and Bundy’s has a better whiff rate (33.7% to 30.2%).

This, a Corbin-esque breakout, is attainable. Bundy just needs to lean into it.

It’s easy to say things will be OK for Bundy, mostly because it’s true. He’s rocking an enormous 15.0% whiff rate, and his 3.68 SIERA suggests that not only a substantial correction looms but also the pitcher who just entered baseball’s history books for all the wrong reasons is still very, very capable. It would also be irresponsible of me to not acknowledge that the effectiveness of a pitcher’s arsenal is a function of how effectively its individual parts interact with one another. I can’t say definitively that Bundy’s slider would still be as effective if he didn’t still throw his terrible fastball half the time. Maybe that’s half the reason his slider looks so good! Who knows.

However, it also stands to reason that even if Bundy’s slider became less effective from throwing it more, the marginal losses suffered in bulk would still substantially improve upon the massive losses continually incurred by his four-seamer. All else equal in 2017, shifting about 18% of his pitches from his four-seamer to his slider (such that he would have thrown his slider 40% of the time, à la Corbin) would have improved his wOBA allowed last year by about 28 points — the equivalent of 0.7 runs knocked off his ERA.* Alas, all else is not truly equal. But given his slider looks better and his fastball looks worse in the early going this year, a similar adjustment to his current pitch mix would cultivate changes in expected wOBA and ERA even more dramatic than those in 2017, at least at this point in time.

* Multiple regression, 379 observations (qualified starters, 2013-17), year fixed effects, r² = 0.79. Roughly, +0.001 wOBA = +0.025 ERA.

So, I’m keeping my eye on Bundy. I have to. If someone in your league made a knee-jerk reaction and dropped Bundy, capitalize on his or her mistake. It’s worth noting Bundy’s not a true-talent 15%-whiff rate guy. And it’s worth reminding you about his extreme fly ball tilt that leaves him perpetually vulnerable to the long ball. But a Corbin-esque paradigm shift — one that happens mid-season — is still in play. The option is on the table, whether Bundy realizes it or not, and I’ll eagerly anticipate his embrace of it.