Regression time for these '19 rooks? Not so fast

Two things are true about Keston Hiura and Fernando Tatis Jr.’s rookie seasons:

1) They were great hitters -- top-25 hitters in all of baseball, in fact, by wRC+. Across 84 games apiece, Hiura hit .303/.368/.570 with 19 homers, and Tatis finished at .317/.379/.590 with 22 dingers.

2) They were lucky, too. Tatis finished with a .410 batting average on balls in play (BABIP) and Hiura at .402, and those marks scream regression because they aren’t sustainable. Mike Trout, the very best hitter in the game, owns a career BABIP of .348.

But at some point, when a hitter keeps driving the ball, he starts creating his own luck. That’s what these two did last year. Hiura and Tatis weren’t your typical slap-hitting rookie middle infielders. They weren’t quite the former “new wave” infielders like Nomar, A-Rod and Jeter, either. They actually looked more like this era’s boom-and-bust slugger, more like an Aaron Judge than a Cal Ripken Jr., and that’s what makes their 2020 seasons a fascinating case study.

First, that regression case …

Start with those BABIPs. Among hitters with at least 250 plate appearances, Tatis led everyone with that .410 mark, while Hiura placed third. Those were two of the 15 highest BABIPs of this century, so yeah, these two found a lot of holes on the diamond. There were also holes in their swings: Hiura and Tatis finished with two of MLB’s 35 highest strikeout rates, and they were both top-20 in whiff-per-swing rate.

Lots of whiffs and strikeouts + sky-high BABIPs = prime regression candidates. Anyone who’s played fantasy baseball has that formula in their head. Hiura finished with a .303 batting average, and yet he struck out in 30.7% of his plate appearances. Tatis hit .317 and struck out 29.6% of the time. If that seems remarkable to you, it was -- those were the two highest strikeout rates (K%) by any .300 hitter on record.

Hiura and Tatis whiffed a ton, as rookies do. But they still slugged … and hit for average … and got on base. That all still seems a bit fluky, especially with those BABIPs in mind.

… but when they connected, they connected

Look closer at the way Hiura and Tatis put those numbers together, and they begin to resemble some current stars. Judge, Joey Gallo and Khris Davis don’t seem to have much in common with Hiura and Tatis, but the rooks took pages right out of those sluggers’ books in 2019:

• They squared the ball up: Half of Hiura’s contact was hard-hit -- 95 mph or harder, per Statcast -- and that tied him with Josh Donaldson and Mitch Garver for seventh in MLB. Tatis was in the 80th percentile with a 44.1% hard-hit rate.

• They elevated, they celebrated: Hit the ball hard, and hit it in the air. That’s what every big leaguer is trying to do, and Hiura and Tatis were among the best. Among hitters with at least 200 batted balls, Hiura tied Juan Soto for the sixth-highest rate of contact that was both hard-hit and in Statcast’s sweet spot zone (the most productive line drives and fly balls – or the “Goldilocks” zone, as MLB.com’s David Adler describes it), ranking only behind Judge, Miguel Sanó, Nelson Cruz, Yordan Alvarez and J.D. Martinez. Tatis was in the top 25%, too.

Hiura and Tatis were also top-25 in barrel rate -- the most ideal contact that usually yields extra-base hits and homers. Statcast’s top-five in barrel rate last year were Sanó, Judge, Cruz, Gary Sánchez and Trout.

• Their damage was largely earned: Tatis slugged .879 on his balls in play, putting him fifth in MLB behind Sanó, Alvarez, Cruz and Christian Yelich. Hiura ranked eighth at .865. That’s another form of BABIP, but, based on the hard air-ball contact mentioned above, Statcast was a believer: Hiura ranked 11th in expected slugging on contact, and Tatis was 29th out of more than 280 hitters.

And it’s not like either guy was cheating for cheapies down the line. Tatis’ spray chart (37% to the pull side / 39% straight ahead / 24% the other way) was nearly identical to the Major League averages. Hiura put the Majors’ third-highest rate of balls right back up the middle.

Live to slug another day

Hard contact and lots of strikeouts have been the recipe for the Judges, Gallos and Cruzes of the world. But, with the possible exceptions of Javier Báez and Max Muncy (when he plays at second base), that was not the recipe for middle infielders -- and certainly not rookie middle infielders -- until now.

From the beginning of the Expansion Era in 1961 through 2018, only 20 rookies overcame a 25% or higher strikeout rate to post a 130-or-higher wRC+. Judge, Cody Bellinger, Ronald Acuña Jr. and Kris Bryant are all on that list. So are previous-generation sluggers like Darryl Strawberry, Fred McGriff and Ryan Howard. What you won’t find? A second baseman or a shortstop. In fact, only three middle infielders of any age -- Báez (2018), Mark Bellhorn ('02) and B.J. Upton ('07) -- pulled off that combo before Hiura and Tatis last year.

As you might expect, Hiura and Tatis were chasers. But they chased efficiently. They recorded the 11th and 12th-worst contact rates on swings outside the strike zone (chase contact %), and that sounds bad. But Judge, Sanó and Jorge Soler (AL-most 48 HRs) were also at the bottom of that list. You’ll find homer kings at the bottom of the 2018 and ’17 leaderboards, too. Last year, Hiura and Tatis chased, whiffed and slugged -- just like the big boppers.

Highest SLG with <45% chase contact%, since 2015
Min. 200 PA
1) .627 – Aaron Judge (2017)
2) .598 – Joey Gallo (2019)
3) .590 – Fernando Tatis Jr. (2019)
4) .576 – Miguel Sanó (2019)
5) .570 – Keston Hiura (2019)

Chases are the bad swings, and heart-of-the-zone swings are the good ones. By missing completely on their bad swings (instead of barely making contact, and topping a soft grounder into play) these “launch sluggers” have, in a way, saved themselves for their best swings later in the at-bat. It only works if you crush your chances, of course, and Hiura and Tatis were extremely good at that in Year 1.

Highest in-zone SLG, 2019
Min. 150 in-zone balls in play
1) Miguel Sanó (MIN): 1.082
2) Fernando Tatis Jr. (SD): 1.028
3) Pete Alonso (NYM): .990
4) Yordan Alvarez (HOU): .988
5) Nelson Cruz (MIN): .966
…
13) Keston Hiura (MIL): .885

The projection systems are conservative on both players; Steamer forecasts a 110 wRC+ for Hiura, and a 112 wRC+ for Tatis. But this pair crushed their way onto too many leaderboards, from box-score stats to swing approaches to contact metrics, to fall all the way back to Earth. We’ve never seen middle infielders -- especially rookies -- go boom and bust to this extreme. There’s no previous example to go off. Maybe they’re bringing something new to the table.