Hitter zStats Through the First Week of June

One of the strange things about projecting baseball players is that even results themselves are small sample sizes. Full seasons result in specific numbers that have minimal predictive value, such as BABIP for pitchers. The predictive value isn’t literally zero — individual seasons form much of the basis of projections, whether math-y ones like ZiPS or simply our personal opinions on how good a player is — but we have to develop tools that improve our ability to explain some of these stats. It’s not enough to know that the number of home runs allowed by a pitcher is volatile; we need to know how and why pitchers allow homers beyond a general sense of pitching poorly or being Jordan Lyles.

Data like that which StatCast provides gives us the ability to get at what’s more elemental, such as exit velocities and launch angles and the like — things that are in themselves more predictive than their end products (the number of homers). StatCast has its own implementation of this kind of exercise in its various “x” stats. ZiPS uses slightly different models with a similar purpose, which I’ve dubbed zStats. (I’m going to make you guess what the z stands for!) The differences in the models can be significant. For example, when talking about grounders, balls hit directly toward the second base bag became singles 48.7% of the time from 2012 to 2019, with 51.0% outs and 0.2% doubles. But grounders hit 16 degrees to the “left” of the bag only became hits 10.6% of the time over the same stretch, while toward the second base side, it was 9.8%. ZiPS uses data like sprint speed when calculating hitter BABIP, because how fast a player is has an effect on BABIP and extra-base hits.

ZiPS doesn’t discard actual stats; the models all improve from knowing the actual numbers in addition to the zStats. You can read more on how zStats relate to actual stats here. For those curious about the r-squared values between zStats and real stats for the offensive components, it’s 0.59 for zBABIP, 0.86 for strikeouts, 0.83 for walks, and 0.78 for homers. Those relationships are what make these stats useful for predicting the future. If you can explain 78% of the variance in home run rate between hitters with no information about how many homers they actually hit, you’ve answered a lot of the riddle. All of these numbers correlate better than the actual numbers with future numbers, though a model that uses both zStats and actual ones, as the full model of ZiPS does, is superior to either by themselves.

But you’re here to see the numbers themselves, not the exposition, so let’s star wipe to the main storyline. I looked at pitcher zStats last week. Today we’ll concern ourselves with hitters.

For the zBABIP chart, I’m sorting by excess/missing hits in play rather than zBABIP itself. ZiPS thinks Luis Arraez ought to be having a dynamite season and a very high BABIP, but sees his current .417 mark as being a bit too high. Overall, the zBA for Arraez comes out at .342, which seems aligned with how we probably should see him, but cruelly takes away the fun of a .400 fight! Of players with at least 100 plate appearances, the zStats actually rank Bo Bichette as the best BA-hitter in baseball, with a .349 BA and a BABIP that’s higher than his real one. If these numbers prove to be more predictive than reality, it’s bad news for Anthony Santander and James Outman, two players you wouldn’t instantly think of as having inflated BAs this year.

I’ve gotten asked a few times about why Keibert Ruiz’s numbers seem so bland relative to how he’s looked at the plate. Well, like the Statcast data (xBA of .296, xSLG of .508), the zStats are on his side, arguably to an even greater degree (zBA .310, zSLG .509). Given his age and talent, if you’re looking for one player to really regress toward the mean with a vengeance, Ruiz is a good candidate. Seeing Julio Rodríguez on the list should also be reassuring given his rather uninspiring sophomore campaign. As you’ll see in a minute, Pete Alonso’s inclusion here is interesting in that ZiPS thinks Alonso is posting the “correct” line this season, but with the completely wrong shape. It’s not a difficult case to make. Wouldn’t it be odd for the Polar Bear to actually have a worse ability to hit unfieldable balls than the average pitcher did?

ZiPS thinks Alonso should be hitting for power, but of the usual 40-homer variety rather than bordering on Aaron Judge. As with Alonso, Bichette is seen by zStats as having a similarly good season to his actual one, but with a very different shape to that contribution. ZiPS thinks Bichette should be a .349/.397/.509 hitter, a rather different shape than .331/.364/.535, but just as valuable. I mean what I said in chat: Bichette should be the long-term contract priority over Vladimir Guerrero Jr. There seem to be a lot of Tampa Bay Rays on this list and that’s something to watch; there was no tendency in the past for the Rays to overachieve with the homers.

Confused by the Vladito power outage? So is ZiPS! He’s still hitting balls hard and in the air; the homers will come. With Spencer Torkelson also an underachiever in other zStats, ZiPS has a different view of the follow-up to his awful rookie season. His 2023 zStat line comes out at a .277/.350/.482 estimated triple-slash! So many of his Statcast/plate discipline stats have improved from last year, we just haven’t seen it manifest in actual performance yet. There may be more hope for Tork than many still hold. As seen above, ZiPS isn’t hyped on Matt Chapman’s batting average, but it does think the power’s been real (when he’s not dealing with an ingrown toenail, at least). It was higher earlier, but across baseball, Chapman has had the fifth most-barrels become outs at 12, behind only Ronald Acuña Jr. and Dansby Swanson at 14, and Bryan Reynolds and Bobby Witt Jr. at 13. Most of those others also finished on this list, and Witt just missed. It’s kind of depressing that ZiPS has José Abreu making this list… and would still only give him a .234/.276/.337 line.

zBB doesn’t see Jake Cronenworth as being deserving of his walk rate bump, which isn’t good news given his struggles this season. There’s better news below. I wouldn’t be alarmed with Juan Soto’s inclusion as he does have a history of overachieving in this stats, so much so that ZiPS nearly ignores his zBB when running a full projection. Mean old ZiPS also takes away the one thing Miguel Cabrera has left!

I’m all for Esteury Ruiz reaching on base even more and thus causing even more stolen base havoc. It’s one of the few watchable things on the A’s this year, though ZiPS takes away a few HBPs to compensate. Bichette’s pattern of either overperforming or underperforming in everything holds true in this case as well. ZiPS doesn’t expect Jazz Chisholm Jr. to continue having such a solid walk rate given how far his contact rate has dipped, down into the low 60s.

What ZiPS gives to Ruiz in walks, it cashes in on strikeouts. What it comes down to is that players with very high first-pitch strike rates don’t tend to strike out a lot more than he actually has. ZiPS also thinks that while Masataka Yoshida should continue to hit for average, his strikeout rate shouldn’t be this low given his plate discipline numbers, which are good but not amazing. The whole z-line for Yoshida (.305/.378/.440) is still very good. There’s a real pattern in these numbers of seeing Andrew McCutchen as the weak part of the Pirates outfield. Connor Joe and Jack Suwinski still end up with an OPS about where their actual numbers are, but the Bucs former franchise player’s line drops to .240/.341/.383, which isn’t all that different from decline-phase Cutch.

Cronenworth appears here, reflecting a real disconnect ZiPS sees between his profile and the actual results, as all his plate discipline numbers suggest someone who puts a lot more balls in play (and thus accrues fewer walks and strikeouts). You’ll notice that Brandon Marsh doesn’t appear in any of the overachiever categories, which indicates that you should probably expect a lot less regression towards the mean than you might think given his huge season; ZiPS actually thinks there’s good reason to believe that he’ll shed some strikeouts. His overall z-stat line of .278/.361/.442 would have sounded preposterous 18 months ago.