Tyler Chatwood and Strikeouts Have a Meet Cute
Suffice it to say, 2018 did not go as anyone predicted or hoped, except maybe Cardinals fans. Chatwood’s season started deceptively well, with a 2.83 ERA in April, but 22 walks in 28 2/3 innings suggested trouble. After throwing seven shutout innings against the Brewers on April 29 of that year, he went three months without a single quality start and walked at least two batters in every game. The team’s acquisition of Cole Hamels resulted in Chatwood’s exile to the bullpen, where he was little-used until injuring his hip in an emergency start as a replacement for Mike Montgomery. A non-factor in the pennant race that September, Chatwood’s 103 2/3 innings of work for the season was still enough time to amass a league-leading 95 walks.
Despite his struggles, it seemed inevitable that Chatwood would be given a second chance at some point; after all, pitchers get hurt. Now in 2020, Hamels is gone, Jose Quintana is out due to an injury sustained while washing his dishes, and the Cubs didn’t sign any free agent starters this past offseason who might have usurped Chatwood’s spot.
As a result, Chatwood’s been given another chance at making the rotation in his walk year, and in two starts, he’s wildly exceeded expectations. Over 12 2/3 innings, he’s only allowed a single run, resulting in two wins for the Cubs. Importantly, neither of these starts were of the nibbling “.150 BABIP Special” variety. Chatwood dominated in both games, striking out 19 batters for a strikeout percentage of 40.4%, more than double his 16.8% career rate. Against the 19 whiffs are just four walks, another unusually positive percentage.
How has he done it? So far, he’s largely removed his vanilla four-seamer from his repertoire, relying heavily on the gruesome twosome of his sinker and cutter. His four-seamer has for the most part been relegated to a change-of-pace pitch, thrown hard and generally high in the zone (or above it), creating a bit of vertical uncertainty in his game plan.
The cutter has been filthy against the team’s NL Central rivals and Chatwood has utilized it as an effective out-pitch:
As for the sinker, it’s largely been a setup pitch for that cutter. Before the season, manager David Ross focused on the sinker as a key for Chatwood:
“Good, Chatty looked good, felt good, had some depth to his sinker,” Ross said. “Said he had felt a little bit like it was more of a runner lately out on the mound today. He got some real good depth to that, felt like he could manipulate the ball both sides.”
Now, two starts is two starts. What does this mean about the future? To project walk and strikeout rates, ZiPS utilizes what I’ve dubbed zBB and zK. Essentially, these are x stats, projecting based on the components rather than the actual rates themselves (I’ll let you figure out why I use a z). Why this approach? Well, because it works. Strikeouts and walks aren’t really single events, just the final tally of a number of individual events during a plate appearance. A strikeout is essentially the cumulative result of hitters not swinging at good pitches, swinging and missing at good pitches, or swinging and missing at bad ones. Strikeouts are merely the “trailing” indicator of the individual moments of the batter-pitcher confrontation.
Contact percentage and swinging strike rate explain roughly 70% of the variation in strikeout rates between pitchers. Other contact variables and pitch data — most notably fastball velocity — also make such a model more accurate. All-in-all, the zK model, generated from data from 2002-2019, has an r-squared of 0.814, essentially meaning that the pitcher-to-pitcher variation in zK% explains 81.4% of the pitcher-to-pitcher variation in actual K%:
So, what does zK say about Chatwood’s performance so far? Good things! Now, zK does think that he’s exceeded expectations by 3.8 strikeouts. That may sound like a lot, but that’s an expected strikeout rate of 32.3%, still about double his career rate. He has not particularly vexed ZiPS in the past, either:
| Year | K% | zK% | Difference |
|---|---|---|---|
| 2011 | 11.7% | 12.4% | -0.7% |
| 2012 | 13.9% | 14.5% | -0.5% |
| 2013 | 13.9% | 15.0% | -1.2% |
| 2016 | 17.5% | 16.2% | 1.2% |
| 2017 | 19.0% | 20.4% | -1.4% |
| 2018 | 17.5% | 18.7% | -1.2% |
| 2019 | 22.8% | 21.4% | 1.5% |
The natural next question is where Chatwood ranks in the league in the early going. Among qualifiers, he’s 10th in the league in zK%:
| Rank | Player | K% | zK% | Diff |
|---|---|---|---|---|
| 1 | Max Scherzer | 39.6% | 42.1% | -2.5% |
| 2 | Sandy Alcantara | 29.2% | 40.1% | -10.9% |
| 3 | Caleb Smith | 20.0% | 39.5% | -19.5% |
| 4 | Zac Gallen | 34.1% | 39.1% | -5.0% |
| 5 | Yu Darvish | 30.0% | 38.6% | -8.6% |
| 6 | Luis Castillo | 33.3% | 36.4% | -3.1% |
| 7 | Sonny Gray | 44.4% | 34.9% | 9.5% |
| 8 | Aaron Nola | 33.3% | 34.1% | -0.8% |
| 9 | Yusei Kikuchi | 34.2% | 32.5% | 1.7% |
| 10 | Tyler Chatwood | 40.4% | 32.3% | 8.1% |
| 11 | Jacob deGrom | 31.6% | 32.2% | -0.6% |
| 12 | German Marquez | 30.4% | 31.8% | -1.4% |
| 13 | Spencer Turnbull | 31.8% | 31.6% | 0.2% |
| 14 | Garrett Richards | 27.9% | 31.4% | -3.5% |
| 15 | Shane Bieber | 54.0% | 30.6% | 23.4% |
| 16 | Wade LeBlanc | 16.7% | 30.6% | -13.9% |
| 17 | Frankie Montas | 20.5% | 30.5% | -10.0% |
| 18 | Dinelson Lamet | 33.3% | 30.1% | 3.2% |
| 19 | Andrew Heaney | 34.3% | 29.8% | 4.4% |
| 20 | Robert Dugger | 11.8% | 29.5% | -17.7% |
Several Marlins make the list, thanks to the innings-pitched qualifiers leading to some odd results. But it’s a good list of guys who have racked up effusive praise in the form of Twitter GIFs!
ZiPS isn’t quite as optimistic about Chatwood’s walk rate. The zBB for Chatwood is 11.8%, also 10th in baseball and almost exactly his career rate. But if he strikes out 12 batters a game, the Cubs will probably not worry about that so much, so long as he doesn’t approach 2018 levels of walkitude.
Can Tyler Chatwood keep it up? Baseball is a game of constant adjustment and if batters start becoming wary of that cutter on the edge of the zone, his early-season results could change quickly. But if he can keep mixing the cutter, sinker, and curve enough to keep batters off-balance, Chatwood could be one of 2020’s big comeback stories.