Pitcher zStats Update for the Stretch Drive
As anyone who does a lot of work with projections could likely tell you, one of the most annoying things about modeling future performance is that results themselves are a small sample size. Individual seasons, even full ones over 162 games, still feature results that are not very predictive, such as a hitter or a pitcher with a BABIP low or high enough to be practically unsustainable. For example, if Luis Arraez finishes the season hitting .333, we don’t actually know that a median projection of .333 was the correct projection going into the season. There’s no divine baseball exchequer to swoop in and let you know whether he’s “actually” a .333 hitter who did what he was supposed to, a .320 hitter who got lucky, or a .380 hitter who suffered extreme misfortune.
If you flip heads on a coin eight times out of 10 and have no reason to believe you have a special coin-flipping ability, you’ll eventually see the split approach 50/50 given a sufficiently large number of coin flips. Convergence in probability is a fairly large academic area that we thankfully do not need to go into here, but for most things in baseball, you never actually get enough coin flips to see this happen. The boundaries of a season are quite strict.
What does this have to do with projections? This volatile data becomes the source of future predictions, and one of the things done in projections is to find things that are not only as predictive as the ordinary stats but also more predictive based on fewer plate appearances or batters faced. Imagine, for example, if body mass index were a wonderful predictor of isolated power. It would be a highly useful one, as changes to it over the course of a season are bound to be rather small. The underlying reasons for performance tend to be more stable than the results, which is why ERA is more volatile than strikeout rate, and why strikeout rate is more volatile than the plate discipline stats that result in strikeout rate.
MLB’s own method comes with an x before the stat, whereas what ZiPS uses internally has a z. (I’ll let you guess what it stands for!) I’ve written more about this stuff in various other places (like here and here), so let’s get right to the data as we start the final third of the season. We’re also looking at how zStats leaders and trailers fared in the two months since I last posted the numbers. Sure, we’re using a small sample size of players and comparing a small sample size to another small sample size, but curiosity gets precedence over everything!
| Name | HR% (6/10) | zHR% (6/10) | HR% Since |
|---|---|---|---|
| José Quintana | 0.9% | 2.7% | 2.4% |
| Merrill Kelly | 1.1% | 2.5% | 2.0% |
| Kevin Gausman | 0.8% | 2.1% | 1.8% |
| MacKenzie Gore | 0.5% | 2.4% | 5.0% |
| A.J. Minter | 0.0% | 4.0% | 2.2% |
| Alex Colomé | 0.0% | 3.7% | 1.1% |
| Bailey Ober | 1.4% | 3.7% | — |
| Shane Bieber | 1.5% | 2.8% | 2.6% |
| Patrick Sandoval | 0.0% | 1.5% | 1.9% |
| Joel Payamps | 0.0% | 3.1% | 6.0% |
| Michael Kopech | 1.0% | 2.5% | 5.3% |
| Kyle Wright | 1.1% | 2.2% | 4.2% |
| Zac Gallen | 1.8% | 3.0% | 2.8% |
| Carlos Carrasco | 1.1% | 2.1% | 3.9% |
| Taylor Hearn | 3.0% | 4.1% | 1.8% |
zHR was closer on 12 of the 14 pitchers here (Ober hasn’t pitched because of a pelvic issue). Remember that zHR doesn’t know how many homers a pitcher was projected to allow or any other standard counting numbers (strikeouts, walks, etc), so unlike a normal projection, it only knows things like how hard balls were hit, what direction/angle, swing data, etc.
| Name | HR% | HR | zHR% | zHR | zHR% Diff | zHR Diff |
|---|---|---|---|---|---|---|
| Kevin Gausman | 1.2% | 6 | 2.8% | 13.5 | -1.5% | -7.5 |
| Merrill Kelly | 1.5% | 8 | 2.8% | 14.6 | -1.3% | -6.6 |
| Alex Colomé | 0.5% | 1 | 3.8% | 7.0 | -3.2% | -6.0 |
| Kyle Freeland | 2.4% | 13 | 3.4% | 18.8 | -1.1% | -5.8 |
| Zach Jackson | 0.6% | 1 | 3.8% | 6.8 | -3.2% | -5.8 |
| Craig Kimbrel | 0.5% | 1 | 3.6% | 6.5 | -3.0% | -5.5 |
| Zach Plesac | 3.0% | 14 | 4.1% | 19.2 | -1.1% | -5.2 |
| José Quintana | 1.7% | 8 | 2.8% | 13.2 | -1.1% | -5.2 |
| Dakota Hudson | 1.8% | 8 | 3.0% | 13.2 | -1.2% | -5.2 |
| Patrick Sandoval | 0.9% | 4 | 2.1% | 9.0 | -1.2% | -5.0 |
| Ross Stripling | 1.8% | 6 | 3.3% | 10.9 | -1.5% | -4.9 |
| Joan Adon | 2.6% | 8 | 4.0% | 12.5 | -1.5% | -4.5 |
| Max Scherzer | 2.2% | 8 | 3.3% | 12.4 | -1.2% | -4.4 |
| Jordan Lyles | 3.1% | 18 | 3.9% | 22.3 | -0.8% | -4.3 |
| Taylor Hearn | 2.6% | 9 | 3.9% | 13.2 | -1.2% | -4.2 |
Naturally, there are going to be a number of repeaters by simple virtue of the fact that when someone has good fortune for a couple of months, you don’t then expect them to be on the schneid for a while; the universe has no physical law of stochastic justice. Freeland is the most prominent newcomer to this list, which is concerning as a pitcher who plays in Coors Field and has never been known for punching out a lot of batters.
| Name | HR% (6/10) | zHR% (6/10) | HR% Since |
|---|---|---|---|
| Elieser Hernandez | 8.3% | 5.4% | 0.0% |
| Hunter Greene | 6.2% | 3.7% | 4.0% |
| Nathan Eovaldi | 5.7% | 3.7% | 3.4% |
| Germán Márquez | 4.3% | 2.6% | 3.2% |
| Shane McClanahan | 3.2% | 1.5% | 2.9% |
| Matt Bush | 5.3% | 1.3% | 0.0% |
| Caleb Smith | 7.0% | 3.8% | 2.9% |
| Beau Brieske | 6.7% | 4.8% | 1.2% |
| Marcus Stroman | 4.0% | 2.4% | 3.2% |
| Kyle Bradish | 6.0% | 4.1% | 2.8% |
| Aaron Sanchez | 4.3% | 2.1% | 0.0% |
| Zack Littell | 5.6% | 2.3% | 5.6% |
| Robbie Ray | 4.7% | 3.7% | 3.1% |
| Marco Gonzales | 4.4% | 3.3% | 3.1% |
| Lucas Giolito | 4.9% | 3.5% | 3.1% |
ZiPS was closer on 13 of 15 here, and only Littell didn’t see an improvement in his gopher ball tendencies. Hernandez has pitched in relief, been injured, and spent time in the minors, so his zero homers have been in only a handful of innings.
| Name | HR% | HR | zHR% | zHR | zHR% Diff | zHR Diff |
|---|---|---|---|---|---|---|
| Josiah Gray | 6.0% | 29 | 4.1% | 19.8 | 1.9% | 9.2 |
| Gerrit Cole | 3.8% | 21 | 2.6% | 14.3 | 1.2% | 6.7 |
| Hunter Greene | 5.2% | 23 | 3.7% | 16.5 | 1.5% | 6.5 |
| Germán Márquez | 3.8% | 20 | 2.8% | 14.9 | 1.0% | 5.1 |
| Spencer Howard | 6.7% | 12 | 3.9% | 7.0 | 2.8% | 5.0 |
| Nathan Eovaldi | 5.0% | 20 | 3.8% | 15.1 | 1.2% | 4.9 |
| Elieser Hernandez | 7.5% | 18 | 5.5% | 13.2 | 2.0% | 4.8 |
| Shane McClanahan | 2.9% | 14 | 1.9% | 9.2 | 1.0% | 4.8 |
| Colin Poche | 5.8% | 9 | 2.9% | 4.5 | 2.9% | 4.5 |
| Jordan Montgomery | 3.1% | 15 | 2.2% | 10.8 | 0.9% | 4.2 |
| Zach Thompson | 4.0% | 16 | 3.0% | 11.9 | 1.0% | 4.1 |
| Corbin Burnes | 3.0% | 16 | 2.2% | 11.9 | 0.8% | 4.1 |
| Kirk McCarty | 8.2% | 8 | 4.2% | 4.1 | 3.9% | 3.9 |
| José Berríos | 4.7% | 24 | 4.0% | 20.1 | 0.8% | 3.9 |
| Matt Bush | 3.0% | 5 | 0.7% | 1.1 | 2.3% | 3.9 |
Gray has allowed 15 homers in the last two months, but ZiPS doesn’t think that he’s deserved quite that many, shooting him to the top of the list after not appearing in June. Cole has allowed just as many over the same time period, but he’s such a dominating pitcher that it hasn’t affected his overall statistics in as obviously alarming a manner. ZiPS is increasingly hopeful about Berríos overall, and new Cardinal Montgomery debuts on this list.
| Name | BB% (6/10) | zBB% (6/10) | BB% Since |
|---|---|---|---|
| Corbin Burnes | 4.9% | 7.9% | 8.5% |
| Antonio Senzatela | 4.8% | 8.4% | 5.9% |
| George Kirby | 2.3% | 7.3% | 3.9% |
| Jameson Taillon | 2.4% | 4.9% | 7.3% |
| Daulton Jefferies | 4.7% | 7.9% | — |
| Paul Blackburn | 6.0% | 8.3% | 6.8% |
| Aaron Nola | 3.4% | 5.3% | 3.7% |
| Craig Stammen | 1.2% | 7.5% | 7.5% |
| Yimi Garcia | 5.7% | 11.6% | 7.1% |
| Evan Phillips | 6.7% | 12.4% | 7.8% |
| Bryan Baker | 7.8% | 12.6% | 12.8% |
| Seth Lugo | 5.0% | 9.7% | 9.9% |
| Cristian Javier | 8.7% | 11.3% | 9.0% |
| Hunter Greene | 10.0% | 11.9% | 8.5% |
| Taylor Clarke | 1.1% | 6.0% | 6.9% |
More mixed results here, with zBB only being closer on six of the 14 chances here. Where zBB was farther away from reality than actual walks in all but one case, the walk rate at least moved in the direction of zBB (which is all ZiPS expects). And I’m quite happy that the pitcher who defied zBB in a positive way was Greene, one of the more exciting raw talents among young pitchers. His ERA has slowly and steadily declined in recent months, and while it still stands inflated above five, he’s had fewer games with control lapses or home run explosions. Since June, his FIP is under four. His zBB% has improved to under 10%, and as such, he’s “graduated” from this ranking.
| Name | BB% | BB | zBB% | zBB | zBB% Diff | zBB Diff |
|---|---|---|---|---|---|---|
| Corbin Burnes | 7.1% | 38 | 9.8% | 52.4 | -2.7% | -14.4 |
| Antonio Senzatela | 5.3% | 20 | 8.1% | 30.6 | -2.8% | -10.6 |
| Lance Lynn | 4.2% | 11 | 7.7% | 20.2 | -3.5% | -9.2 |
| Paul Blackburn | 6.4% | 30 | 8.4% | 39.1 | -1.9% | -9.1 |
| Max Fried | 4.5% | 25 | 6.1% | 34.0 | -1.6% | -9.0 |
| Josiah Gray | 9.5% | 46 | 11.3% | 54.4 | -1.7% | -8.4 |
| George Kirby | 3.3% | 11 | 5.8% | 19.4 | -2.5% | -8.4 |
| Taylor Clarke | 4.1% | 8 | 8.4% | 16.4 | -4.3% | -8.4 |
| Jameson Taillon | 4.8% | 24 | 6.4% | 31.9 | -1.6% | -7.9 |
| Rony Garcia | 6.3% | 13 | 10.0% | 20.7 | -3.7% | -7.7 |
| Craig Stammen | 3.6% | 5 | 9.2% | 12.7 | -5.6% | -7.7 |
| Liam Hendriks | 5.7% | 9 | 10.6% | 16.6 | -4.8% | -7.6 |
| Yu Darvish | 4.8% | 26 | 6.2% | 33.6 | -1.4% | -7.6 |
| Paolo Espino | 4.1% | 13 | 6.4% | 20.5 | -2.4% | -7.5 |
| Yimi Garcia | 6.3% | 10 | 11.0% | 17.4 | -4.7% | -7.4 |
Burnes is having a very good season, though not one on the level of his Cy Young award-winning 2022. He’s already walked more batters than he did all of last year, and his zBB% has deteriorated further since June. White Sox fans obviously have quite a lot to be concerned about, so the idea that Lynn might be overachieving in his walk rate is probably not the analysis tidbit any are eager to hear. But there’s good news: ZiPS thinks he’s underachieving elsewhere and actually deserves a FIP of 4.32, about a third of a run better than his actual FIP of 4.63.
| Name | BB% (6/10) | zBB% (6/10) | BB% Since |
|---|---|---|---|
| Merrill Kelly | 9.9% | 6.5% | 4.7% |
| Joan Adon | 13.2% | 10.0% | 9.1% |
| Sean Manaea | 8.7% | 6.0% | 8.6% |
| Nick Martinez | 10.5% | 7.0% | 6.3% |
| Framber Valdez | 8.9% | 6.4% | 8.4% |
| Taylor Hearn | 10.8% | 7.7% | 8.2% |
| Adam Wainwright | 8.2% | 5.6% | 5.6% |
| Hunter Strickland | 16.5% | 9.9% | 7.6% |
| Yusei Kikuchi | 13.5% | 10.5% | 12.4% |
| Dillon Peters | 15.4% | 9.3% | 1.6% |
| Spencer Strider | 13.5% | 8.9% | 7.0% |
| Cal Quantrill | 8.1% | 5.7% | 5.6% |
| Dylan Cease | 12.0% | 9.7% | 8.5% |
| Daniel Lynch | 9.9% | 7.4% | 7.2% |
| Aaron Ashby | 11.2% | 8.4% | 10.2% |
On this list, zBB was closer on 11 of 15 pitchers.
| Name | BB% | BB | zBB% | zBB | zBB% Diff | zBB Diff |
|---|---|---|---|---|---|---|
| Sean Manaea | 8.6% | 44 | 6.2% | 31.6 | 2.4% | 12.4 |
| Joely Rodríguez | 15.1% | 21 | 7.2% | 10.0 | 7.9% | 11.0 |
| Matt Moore | 12.9% | 28 | 7.9% | 17.1 | 5.0% | 10.9 |
| Joan Adon | 12.6% | 39 | 9.6% | 29.6 | 3.0% | 9.4 |
| Matt Brash | 16.9% | 24 | 10.9% | 15.4 | 6.0% | 8.6 |
| Merrill Kelly | 7.4% | 39 | 5.8% | 30.5 | 1.6% | 8.5 |
| Aaron Ashby | 10.7% | 41 | 8.5% | 32.5 | 2.2% | 8.5 |
| Will Smith | 11.2% | 21 | 6.8% | 12.7 | 4.5% | 8.3 |
| Patrick Sandoval | 10.6% | 45 | 8.7% | 36.9 | 1.9% | 8.1 |
| Caleb Smith | 13.3% | 29 | 9.6% | 20.9 | 3.7% | 8.1 |
| Trevor Rogers | 10.3% | 41 | 8.2% | 32.9 | 2.0% | 8.1 |
| Marco Gonzales | 7.4% | 40 | 6.0% | 32.3 | 1.4% | 7.7 |
| Kris Bubic | 11.2% | 43 | 9.2% | 35.5 | 2.0% | 7.5 |
| José Berríos | 5.7% | 29 | 4.3% | 21.7 | 1.4% | 7.3 |
| Germán Márquez | 8.1% | 43 | 6.8% | 35.7 | 1.4% | 7.3 |
Manaea continues to befuddle ZiPS, as it just doesn’t see in the contact data why his walk rate has had a bump this season. He’s been weirdly ineffective after allowing a first-pitch ball this season, with an OPS more than 200 points higher after 1–0 than league average. One has to wonder if there’s an approach problem, something that might be fun to dig into.
| Name | SO% (6/10) | zSO% (6/10) | SO% Since |
|---|---|---|---|
| Nestor Cortes | 28.6% | 21.8% | 24.7% |
| Rony García | 30.0% | 17.8% | 15.6% |
| Cristian Javier | 30.4% | 23.7% | 34.2% |
| Frankie Montas | 27.9% | 23.5% | 20.5% |
| Austin Gomber | 17.9% | 12.6% | 17.5% |
| Aaron Nola | 29.3% | 25.2% | 26.4% |
| Justin Verlander | 27.0% | 22.7% | 24.2% |
| MacKenzie Gore | 30.0% | 24.5% | 12.6% |
| Eric Lauer | 27.7% | 23.4% | 19.7% |
| Joan Adon | 16.5% | 13.1% | 25.0% |
| Yusei Kikuchi | 25.1% | 20.8% | 24.8% |
| Carlos Rodón | 30.2% | 26.6% | 32.1% |
| Eli Morgan | 35.1% | 25.9% | 25.9% |
| Robert Suarez | 30.9% | 21.5% | 0.0% |
| Emmanuel Clase | 29.7% | 20.2% | 27.1% |
ZiPS was closer on nine of 15, though we might as well call it eight of 14 since Suarez just got back from knee surgery and has pitched in just a couple of games. Javier and Carlos Rodón pulled the ol’ topsy-turvy trick on zSO, with their strikeout rates going in the opposite direction. zSO is still skeptical about Javier being quite this good, but it’s much less so with Rodón, as his seasonal zSO% has surged a full four percentage points since June. In other words, Rodón really has been killing it. He’s a serious Cy Young contender now, at least on my ballot (if I should vote in this award; we don’t know until September).
| Name | SO% | SO | zSO% | zSO | zSO% Diff | zSO Diff |
|---|---|---|---|---|---|---|
| Spencer Strider | 38.0% | 138 | 31.1% | 113.1 | 6.9% | 24.9 |
| Justin Steele | 23.7% | 106 | 18.4% | 82.2 | 5.3% | 23.8 |
| Robbie Ray | 28.0% | 156 | 23.8% | 132.7 | 4.2% | 23.3 |
| Cristian Javier | 32.5% | 132 | 27.4% | 111.4 | 5.1% | 20.6 |
| Zac Gallen | 23.9% | 114 | 20.3% | 96.6 | 3.6% | 17.4 |
| Nestor Cortes | 26.8% | 125 | 23.2% | 108.5 | 3.5% | 16.5 |
| Frankie Montas | 25.2% | 111 | 21.5% | 94.9 | 3.7% | 16.1 |
| Zack Wheeler | 27.2% | 137 | 24.1% | 121.7 | 3.0% | 15.3 |
| Rony García | 23.3% | 48 | 16.4% | 33.7 | 6.9% | 14.3 |
| Justin Verlander | 25.7% | 134 | 23.0% | 119.8 | 2.7% | 14.2 |
| Yusei Kikuchi | 25.0% | 88 | 21.2% | 74.6 | 3.8% | 13.4 |
| David Peterson | 27.2% | 91 | 23.5% | 78.7 | 3.7% | 12.3 |
| Aaron Nola | 27.9% | 157 | 25.7% | 144.7 | 2.2% | 12.3 |
| Sean Manaea | 24.0% | 122 | 21.6% | 110.2 | 2.3% | 11.8 |
| Penn Murfee | 30.1% | 56 | 24.0% | 44.7 | 6.1% | 11.3 |
zSO is coming around on Cortes, as both his actual rate and the estimates one are much closer to converging than in June. Seeing Strider shoot to the top of this list isn’t actually concerning, as it still amounts to 11 strikeouts a game for a rookie who had one game above Double-A ball coming into the season.
| Name | SO% (6/10) | zSO% (6/10) | SO% Since |
|---|---|---|---|
| Jordan Montgomery | 19.4% | 25.9% | 20.9% |
| Yu Darvish | 20.1% | 25.8% | 28.9% |
| Carlos Hernández | 10.7% | 19.7% | 10.0% |
| Tyler Wells | 15.3% | 22.1% | 20.2% |
| Noah Syndergaard | 15.4% | 21.6% | 20.8% |
| Chad Kuhl | 18.2% | 22.8% | 14.9% |
| Zack Greinke | 11.2% | 15.8% | 15.6% |
| Kyle Hendricks | 14.8% | 18.8% | 27.4% |
| Paul Blackburn | 18.9% | 23.0% | 19.2% |
| Dany Jiménez | 24.2% | 34.4% | 31.3% |
| Spenser Watkins | 10.0% | 16.5% | 19.7% |
| Taijuan Walker | 12.9% | 16.9% | 23.0% |
| Griffin Jax | 26.1% | 32.5% | 28.4% |
| Steven Wilson | 22.6% | 31.3% | 27.1% |
| Domingo Acevedo | 20.6% | 27.2% | 23.3% |
Nine of 15 again for zSO, though no Suarez cheats this time. I was most personally worried in June to see Greinke here, given his age and the fact that he relies less on stuff and more on moxie, knowhow, and other words used to describe every old lefty pitcher in 1934. Thankfully, the forced end of his career looks less obvious, and if you haven’t been paying too much attention to the Royals since June — and it’s perfectly OK if you haven’t — Greinke’s pitched quite well. It’s also nice to see Syndergaard match his stat — hopefully a sign that he’s slowly getting used to smiting mortals without the benefit of thunderbolts.
| Name | SO% | SO | zSO% | zSO | zSO% Diff | zSO Diff |
|---|---|---|---|---|---|---|
| Jordan Montgomery | 20.2% | 98 | 26.3% | 128.0 | -6.2% | -30.0 |
| Tyler Wells | 17.8% | 68 | 21.5% | 82.5 | -3.8% | -14.5 |
| Carlos Hernández | 10.7% | 18 | 19.2% | 32.5 | -8.6% | -14.5 |
| Josh Winder | 15.3% | 29 | 22.9% | 43.4 | -7.6% | -14.4 |
| Sammy Long | 18.2% | 33 | 24.9% | 45.1 | -6.7% | -12.1 |
| Wandy Peralta | 19.4% | 34 | 26.3% | 46.0 | -6.9% | -12.0 |
| Tyler Anderson | 20.1% | 97 | 22.5% | 108.5 | -2.4% | -11.5 |
| Zack Greinke | 13.1% | 52 | 16.0% | 63.3 | -2.9% | -11.3 |
| Aaron Ashby | 26.9% | 103 | 29.8% | 114.3 | -2.9% | -11.3 |
| Chad Kuhl | 16.5% | 76 | 19.0% | 87.3 | -2.4% | -11.3 |
| Chris Bassitt | 24.2% | 129 | 26.3% | 140.0 | -2.1% | -11.0 |
| Domingo Acevedo | 21.8% | 43 | 27.1% | 53.5 | -5.3% | -10.5 |
| Spenser Watkins | 15.2% | 45 | 18.6% | 55.4 | -3.5% | -10.4 |
| Shane Bieber | 25.4% | 134 | 27.3% | 144.2 | -1.9% | -10.2 |
| Ty Blach | 12.2% | 21 | 18.1% | 31.2 | -5.9% | -10.2 |
The continued presence of Montgomery dominating here is something I just don’t know how to make sense of. He’s not a pitcher who has a history of outperforming in this measurement, yet he’s more than doubling up the total of the second-place pitcher on the list. He certainly doesn’t look all that different to me, and the primary change in his pitching style this year has been a lot more sinkers (especially on strike three) than four-seamers and cutters, but in truth, none of these pitches are whiff-inducers anyway. He’s already nearly at the largest discrepancy going back to 2002 of any pitcher, the current record holder being Kevin Gausman at 34 strikeouts in 2008 (148 actual versus 182 zSO). It worked out for Gausman at least, as his strikeout rate improved from 19.1% then to 28.4% since. I hate when I don’t understand something.
Dan Szymborski is a senior writer for FanGraphs and the developer of the ZiPS projection system. He was a writer for ESPN.com from 2010-2018, a regular guest on a number of radio shows and podcasts, and a voting BBWAA member. He also maintains a terrible Twitter account at @DSzymborski.
Monty’s sinker usage is way, way up this season. Maybe he’s just going for more groundballs than strikeouts?