Since coming over to the Cubs at the trade deadline, Codi Heuer has been nothing short of fantastic. From the date of his first appearance on the north side (July 31st), his 1.40 ERA ranks 23rd in MLB, and no one ahead of him on that list has thrown more than his 25.2 innings of work.
When I was digging in on his numbers, however, I noticed that at least one of his higher-level peripherals over his time with the Cubs (4.10 FIP) was quite a bit higher than his actual results (as well as his 3.20 FIP from last season). And that felt worth exploring.
Fielding Independent Pitching (FIP) is scaled to look somewhat similar to ERA, but it focuses solely on events within a pitcher’s control (strikeouts, unintentional walks, HBPs, home runs). And while it is imperfect in many ways, it can steer your attention to some other issues. For example, Heuer’s strikeout rate has dropped from 23.5% with the White Sox this season to just 16.7% with the Cubs. Meanwhile, his walk rate has increase from 6.0% on the south side to 9.4% in the north. At face, those numbers are not good. Alarming, even!
It’s undoubtedly something to keep an eye on — any potential high-leverage reliever needs to have a strikeout rate well above 16.7% (and you never want your walk rate to climb) — but obviously Heuer has nonetheless found success. And that’s not all that uncommon. Plenty of pitchers routinely “outperform” their FIP, but that usually requires a great deal of contact management success, which is where we’re headed next.
Compared to his first half with the Sox, Heuer is generating more ground balls, more infield pop-ups, more soft contact, less hard contact, a lower average exit velocity, and a smaller barrel rate. The short version of that data? Batters may be making more contact overall now that Heuer is with the Cubs, but the quality of that contact is significantly worse. And that appears to explain at least some of the difference between his 2021 results with the Sox (5.12 ERA over 38.2 IP) versus the Cubs (1.40 ERA over 25.2 IP). There’s probably some luck in there, too, but credit where it’s due. Generating crappy contact is a repeatable skill.
So, okay, great. We know why his results have been so much better than his peripherals, but that’s not enough. Now I want to know how he’s doing it. In other words, how has he been able to so greatly reduce the quality of contact batters are making against him this season with the Cubs? Has THAT part been the good luck, or is he actually doing something differently? And to answer that, at least in part, we turn to the pitch mix (all data via PitchInfo).
Consider a couple of his pitches …
2020 White Sox: 65.5%
2021 White Sox: 53.1%
2021 Cubs: 63.0%
2020 White Sox: 9.3%
2021 White Sox: 22.9%
2021 Cubs: 13.9%
Note: Heuer also throws a slider around 24% of the time (so it is definitely not an insignificant part of his story), but he’s kept that usage mostly level over the past two seasons. So for today, we’ll focus solely on changes to his usage of the fastball and changeup.
As you can see, Heuer’s changeup usage has dropped rather dramatically with the Cubs, replaced almost entirely by his fastball, which he’s throwing more often, but at a slightly lower velocity (96.5 MPH vs. 95.1 MPH). This mix more closely matches his rookie approach with the White Sox in 2020, when he was extremely successful over 23.1 IP in terms of results and peripherals: 1.52 ERA, 3.20 FIP. So right on the surface, you might be willing to think this is all pretty simple: The White Sox must’ve tweaked his pitch mix this season, but after it didn’t work, the Cubs went back to what he was doing in 2020.
But it’s not that easy.
Considering that his changeup has historically been a much more dependable swing-and-miss pitch than his fastball, it’s not all that surprising to see his strikeout rate evaporate alongside the change. What is surprising, however, is that the (1) expected batting average, (2) expected slugging percentage, (3) average exit velocity, (4) launch angle, and (5) overall xwOBA of his four-seamer are all higher than his changeup … which is exactly the opposite thing you might’ve otherwise expected given the trends in his pitch usage and contact data.
But what the data doesn’t tell us, Sahadev Sharma (The Athletic) will (emphasis mine): “What stands out with him, at least for now, is the lack of swing-and-miss. Heuer is adjusting to using a new arsenal — he’s throwing two fastballs now, a four-seamer and two-seamer, both of which have a decent amount of run to them due to his low three-quarters arm slot.”
Okay, now we’re getting somewhere. You may recall discussion when Heuer first came over about how his fastball was kinda bleeding into two versions, albeit not necessarily intentionally. Although FanGraphs, PitchInfo, and Statcast are still not yet separating Heuer’s two-seamer and four-seamer (perhaps because he hasn’t yet thrown many?), Sharma reports that he is now definitely throwing throwing both.
The Cubs appear to be keeping the overall fastball usage (both pitches combined) around the same rate for now — a rate which worked well for him last season — but perhaps he’s breaking out the two-seamer for a little extra weak contact on the margins (which could help explain the overall drop in reported fastball velocity, as well as the contact quality). Or perhaps they simply play well off one another (or against other pitches in his arsenal) to accomplish the same goal.
Ultimately, it seems as though he’ll need to tick the changeup usage back up a little bit to reintroduce more swing and miss to his game when the time is right (and/or see further improvements in the slider), but the Cubs may have already found a way to use what was working for him last season and take his entire approach up to another level. That wouldn’t be surprising, given how much he reportedly mattered to the Craig Kimbrel deal getting done in the first place.
So what am I really saying here? The Cubs have tweaked Codi Heuer’s pitch mix to more closely align with his successful 2020 campaign with the White Sox while also introducing a two-seamer to take him to another level. And considering how well it’s already worked out despite the strikeout rate lag, it seems to be a very good plan for 2022 and beyond.