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Which MLB Players Could Regress to the Mean in the Second Half?

For some, that means returning to a previous standard of excellence. For others, it’s not as promising.

Getty Images/Ringer illustration

Regression to the mean sounds like a bad thing. Specifically, it sounds like when you go home to visit your parents for Thanksgiving and instead of acting like grown-ups who love each other, everyone reverts to the same level of hostility and tension that filled the house when you were 17. In baseball terms, “regression to the mean” is a concept adapted from statistics: A small data sample can yield extreme results, but as time goes on, the vicissitudes of chance even out and player or team performance tends to conform to previous expectations. Someone who’s playing over his head could come crashing back to Earth, yes, but a good player in a slump could also be said to regress back to his previous standard of excellence.

In the grand scheme of things, even a half-season isn’t that big a sample, and in 2019 we’ve seen all manner of unexpected performances, for good and ill. Here are four players who ought to see their fortunes change in the coming months.

José Ramírez, Cleveland Indians

Cleveland started the season with an 80.8 percent chance of winning the AL Central, according to Baseball Prospectus, and, well, in the past three and a half months the other 19.2 percent has come up huge. Most of the reasons for Cleveland’s disappointing first half are obvious: The Twins are way better than anticipated. Cleveland didn’t bother to sign any outfielders last offseason. Francisco Lindor and Mike Clevinger spent some time on the IL. Corey Kluber is still on the IL and might not make it back before the last few weeks of the season, and the same goes for Carlos Carrasco, who is undergoing treatment for leukemia.

But Ramírez’s annus horribilis is somewhat harder to explain. Ramírez finished third in AL MVP voting in both 2017 and 2018, and over those two years combined he hit .294/.380/.567 while averaging 34 home runs, 26 stolen bases, and 7.3 bWAR. This year, however, Ramírez is hitting just .218/.308/.344, which is his worst batting line since 2015 and just half a win above replacement.

There are, however, reasons to believe he’ll get back to at least league average or better, if not his lofty standards of 2017 and 2018. Every year from 2016 to 2018, Ramírez’s batted-ball profile has evolved to favor fly balls, from a 1.32 ground-ball-to-fly-ball ratio in 2015 to a ratio of 0.73 in 2018. Ramírez has increased his ISO and home run totals in each year of that evolution, and his walk rate jumped to a career high of 15.2 percent in 2018. His GB/FB ratio this year is 0.66, and his hard-contact rate is almost exactly the same as it was last year.

Despite that, his wRC+ has plummeted from 146 in 2018 to 69 in 2019. Now, Ramírez is walking less than he was last year, and striking out a little more, but there’s also substantial evidence that he’s getting unlucky. A fly-ball-heavy profile leads to a lower BABIP, which explains why his BABIP last year, .252, was more than 80 points lower than what it was in 2016. This year, it’s all the way down to .234, the eighth-lowest in baseball among 157 qualified hitters. His HR/FB rate has also dropped to less than a third of what it was in 2018; if his fly balls were leaving the yard at the level they were last year, he’d have 22 homers at the break, not seven.

Baseball Savant uses Statcast data to estimate a deserved wOBA for hitters based on the batted balls they produced; Ramírez has the 17th-largest negative differential between xwOBA and wOBA out of 359 players with at least 100 plate appearances.

Ramírez has, in fact, already started to turn his season around, hitting .284/.353/.514 since June 14. That’s not quite up to his standards from previous years, but if he can produce at that level down the stretch, Cleveland will be in good shape.

Scott Kingery, Philadelphia Phillies

Kingery is the Bizarro World version of Ramírez. Both players are short, came up as middle infielders, and ended up playing all over the field. Both are signed to long-term, extremely team-friendly contracts. But while Ramírez was an MVP-caliber player in 2018 who forgot how to hit this year, Kingery was … well … not literally the worst player in baseball, but close. As a rookie, Kingery hit just .226/.267/.338, but the Phillies were so hard-up for help at shortstop that he got into 147 games, most of them at a defensive position he wasn’t equipped to handle.

In 2019, Kingery has stepped back into the lineup, not at his natural position of second base, but at center field, where he’s filled in following Odubel Herrera’s suspension and injuries to Andrew McCutchen and Adam Haseley.

And Kingery has thrived. He’s hitting .292/.344/.545 and has a higher OPS+ than Bryce Harper, Jean Segura, McCutchen, or J.T. Realmuto, the four sluggers the Phillies acquired this offseason. Now, a lot of Kingery’s improvement can be explained by the fact that he’s hitting the ball much harder (49.6 percent hard-contact rate in 2019, up from 26.6 in 2018). As a result, his BABIP and HR/FB ratio are up substantially from last year, 78 points and 14.8 percentage points, respectively. But both of those increases are so big it indicates that Kingery’s getting at least somewhat lucky.

Kingery is 30th in positive differential on the xwOBA-wOBA discrepancy leaderboard, continuing his mirror-image season of Ramírez. And like Ramírez, he’s already started to slide back to normal since mid-June: In his past 17 games, he is hitting .208/.288/.333. Kingery isn’t headed back to his 2018 level of production—his underlying numbers are still above average—but don’t expect him to keep outhitting Harper in the second half.

Zach Davies, Milwaukee Brewers

Davies has also started his slide back to normal before the break: After keeping his ERA in the mid-1.00s through mid-May, he’s allowed 24 earned runs in 44 innings in his past nine starts, split more or less into great outings, decent outings, and disastrous outings. Keeping a low ERA over a full season demands more consistent excellence than posting gaudy strikeout totals, because just one bad outing can goose a pitcher’s ERA by a run or more.

Davies entered the break with a 3.07 ERA, 10th among qualified MLB starters, and has been a huge help in a Brewers rotation that’s gotten only nine combined starts from Jimmy Nelson and Gio González, and has had to make up for Corbin Burnes and Jhoulys Chacín handing out home runs like Solo cups of Natty Light at a high school senior’s house party.

But Davies, who’s never been a big strikeout guy, is third from the bottom in strikeout rate among qualified starters. His strand rate, 79.4 percent, is 10th in MLB and the highest of his career, and ERA estimators say he’s got a way to fall even from his current mark of 3.07. Davies’s FIP is 4.37 and his DRA is a staggering 5.50. It seems odd to say this about someone who was leading the NL in ERA not too long ago, but if Davies doesn’t keep finding ways to dodge his peripherals, he could be out of Milwaukee’s rotation by season’s end.

Edwin Díaz, New York Mets

Díaz converted his first 12 save chances in a Mets uniform before blowing his first save on May 25. Since that date, he is 0-4 with a 10.43 ERA, with four blown saves in 11 chances. Opponents are hitting .385/.431/.662 off Díaz in that 16-game stretch.

Last year, Díaz struck out 124 batters in 73 1/3 innings, converted 57 saves from 61 chances, and posted a 1.96 ERA while actually underperforming his DRA, which had him pegged at 1.77. It’s painfully obvious that the guy who posted those numbers a year ago will not continue to turn the average MLB hitter into prime Rogers Hornsby all through the second half. Indeed, even in this, the winter of Díaz’s discontent, with his season ERA at 5.50, his strikeout numbers (37.1 percent K rate) are excellent by anyone else’s standards, and while his DRA is up this year, it’s up to only 2.74.

Even in his terrible six-week stretch, Díaz’s fastball velocity has been fine and his strikeout rate is in line with his season average. But he’s been getting unfathomably unlucky. Since May 25, opponents have tagged Díaz for a BABIP of .583 and almost half of the runners who have reached against him have come around to score. He’s allowed just 16 fly balls in that span, but four of them have turned into home runs.

Díaz is allowing a higher-than-average hard-contact rate in that span, and since May 25, opponents have stolen eight bases off him without being caught, so some of this trouble is of his own making, but it’s exacerbated by his surroundings. Díaz’s blown saves have caused some of the capstone losses in a stretch in which the Mets are coming apart from within, in which their leadership, from ownership to GM Brodie Van Wagenen to manager Mickey Callaway, is giving off some serious last-days-of-empire vibes.

Díaz is also one of the faces of a failed first offseason under Van Wagenen, as he and Robinson Canó were acquired from Seattle in a win-now move that sent flourishing prospects Jarred Kelenic and Justin Dunn the other way. Each save Díaz blows kicks off a wave of complaints from a fan base renowned for its capacity for self-pity, echoed in one of the most intense local sports media markets in the Western Hemisphere. These recriminations turn back around on the trade for Díaz, which is now something of a historical flashpoint that kicked off this lost year in the first place. Kelenic hits a home run in A-ball, Díaz blows a save, the cycle renews itself …


… well, you get the idea.

The Mets’ general state of dysfunction makes it hard to guarantee that Díaz will return to form—maybe he’s nursing an undisclosed injury, or maybe he’s catching stray bad vibes from the witch who put a curse on Van Wagenen. But at the risk of sounding reductive, he’s simply too good to continue pitching this badly for much longer.