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How seriously should we take Paul DeJong?

For the second consecutive season, the big breakout Cardinal is a rookie shortstop. Will this one keep it up?

MLB: Atlanta Braves at St. Louis Cardinals Jeff Curry-USA TODAY Sports

That Tommy Pham is leading the St. Louis Cardinals in Wins Above Replacement in 2017 after beginning the season in AAA Memphis is a huge surprise, one of the biggest surprises in baseball this season. But Pham had at least shown glimpses of potential at the Major League level—it would take quite a bit of squinting, but one could eventually see him as the team’s MVP being at least possible.

Relative to the sheer absurdity which is Paul DeJong’s breakthrough with the Cardinals in 2017, that is.

Paul DeJong made his MLB debut on May 28 of this season against the Colorado Rockies, and he hit a home run—as an aside about which you assuredly do not care, I missed the home run, because the Cardinals were being blown out and it was a beautiful late Spring day so I went outside. When I heard what had happened, I regretted that I missed what, for all we knew, could be the only home run of DeJong’s career.

After all, while DeJong’s raw power was generally considered his strongest skill, he was not considered a can’t-miss prospect. Baseball America ranked DeJong as the 14th best Cardinals prospect after the 2016 season, a slight bump from his #16 ranking after 2015. John Sickels ranked DeJong 10th. An aggregate ranking compiled by Ben Markham in March ranked DeJong at 12. Viva El Birdos prospect guru the red baron ranked the Illinois State product 11th, while fellow minor league aficionado Josey Curtis was the most bullish, ranking him eighth.

Anyway, my fears that I had missed the lone home run of his career were quickly and emphatically put to rest (fun fact: the most recent position player to hit his lone career home run with the Cardinals, not counting the still-active Alex Mejia, was catcher Matt Pagnozzi in 2010). With eighteen home runs in the less than three months since his promotion to St. Louis, DeJong leads the Cardinals in the category.

Despite his late start, Paul DeJong trails only Aaron Judge and Cody Bellinger among rookie position players in FanGraphs Wins Above Replacement. DeJong is also only trailing the aforementioned Yankees and Dodgers Rookie of the Year front-runners in wRC+ among players with as many plate appearances as DeJong.

In addition to his offensive prowess, DeJong has been one of baseball’s most valuable rookies defensively, which has been arguably an even bigger surprise. After all, DeJong had spent his minor league career primarily as a third baseman prior to 2017, and he has spent most of his time in St. Louis playing a more difficult defensive position in shortstop. And yet, despite this additional responsibility, DeJong has been a plus defender at shortstop.

It was just one year ago that a different young shortstop, one whose ability to play the position at a Major League level had been an open question and one who began the season in AAA, was taking the Cardinals by storm. Aledmys Diaz was an All-Star, he finished 2016 with 460 plate appearances and a batting season which was 32% above average, and while his defense was sub-par, it was tolerable given his offensive production.

But then in 2017, Aledmys Diaz struggled. His walk rate was halved, his power declined, his defense was actually slightly better statistically but it was far from exceptional. Suddenly, with an offensive downturn, Diaz felt like Ryan Theriot—if he had more of a glove, the team could look past his offensive mediocrity, but in the meantime, Diaz was sent to the minors, and with Paul DeJong as hot as he has been, he may be there for a while.

The Cardinals have been seduced by small sample size success from shortstops before, but sticking with Diaz entering 2017 was defensible. While some regression was expected, he showed signs of authenticity in his rookie year—his BABIP was a high but not unfathomable .312 and he appeared more comfortable defensively in the latter stages of 2016 than when he was rushed into the starting lineup. Additionally, there were alternatives to Diaz if things went wrong beyond DeJong—between recent starting shortstop Jhonny Peralta, occasional spot starter Jedd Gyorko, and utility player Greg Garcia, it seemed that somebody could at least be serviceable if the worst happened with Diaz.

The ultimate recent example of small sample size magic fooling the Cardinals at shortstop was Pete Kozma. Following a 2012 injury to Rafael Furcal, the former first-round pick Kozma was called up and had a truly special abbreviated season: 152 wRC+, solid defense, a fWAR rate that over a 600 plate appearance pace would put him at 9.5 fWAR, which would be considered best-player-in-baseball level performance had this not also been Mike Trout’s rookie season.

After it was determined that Furcal would miss 2013 due to injury, Kozma became the full-time starter and, well, his defense was good! And he was a (slightly) above-average base runner! However, his wretched 49 wRC+ meant that the Cardinals were very eager to replace him with Jhonny Peralta in 2014.

With Kozma and Diaz as recent precedent, it is fair to be concerned about overrating Paul DeJong. It is fair to look at his relatively pedestrian prospect pedigree and see an aberration. But this would also be an absurd generalization, one borne of an inherent fatalism and a belief that the Cardinals are doomed to never produce a worthwhile shortstop of their own. Players do emerge from circumstances other than being a top draft pick—it just isn’t a guarantee. So in theory DeJong could be for real—it just requires further examination to determine whether this is the case.

An important factor which I hinted at before but which merits mentioning again: it’s not like Paul DeJong never hit a home run before 2017. DeJong hit 22 in AA Springfield last season, and in 190 plate appearances in Memphis in 2017, he hit 13 homers. DeJong hit home runs in Springfield at a faster rate than fellow rookie Luke Voit, and hit more home runs than any other players in Springfield since 2013 Xavier Scruggs. Unfortunately, Scruggs has hit a total of one home run in his MLB career (with the Miami Marlins, in case you were concerned I was contradicting my previously cited fun fact); these numbers don’t necessarily reflect MLB success.

At this point, DeJong’s batting average on balls in play stands at .376. He is not an especially fast runner, so it is not as though he is simply beating out a disproportionate number of ground balls. Looking at his contact quality, his expected BABIP is somewhere closer to .315—slightly above-average, but not one which would produce nearly the results of a .376 BABIP.

Perhaps the most jolting individual batted ball metric of DeJong’s is his 24.3% home run to fly ball ratio. While the league-wide HR/FB% rate has increased over the last couple seasons, the league-wide 13.7% rate is staggeringly behind DeJong’s. Rather than hitting home runs at a 40 dinger pace over a full season, a normalized home run total assuming league-average home run to fly ball rates is in the twenties—again, still fine, but not as enticing when coupled with a low walk rate, common batted-ball luck, and defense which may or may not be serviceable once we examine a larger set of data.

DeJong’s defensive numbers have been good at the MLB level, but in a very small time frame. That he only recently was moved to shortstop is not a great sign for his long-term viability, or seemingly he would have been moved there long ago, but it’s arguably a more promising situation than what the Cardinals had with Diaz—after all, DeJong’s conversion was spurred by his exceeding expectations, whereas rumors of Aledmys Diaz shifting to second or third base were an indictment of unspectacular results. But expecting him to be anything about competent at the position seems a bit optimistic.

While Paul DeJong probably isn’t going to keep this up, he has a considerably more promising outlook than Pete Kozma had, and there is a bit more reason to believe in him than in Aledmys Diaz. After all, Paul DeJong’s power appears to be at least somewhat for real, even if it turns out he’s not a 40 home run hitting shortstop (note: there have been twelve 40+ home run seasons by shortstops in MLB history, and eleven were by either Alex Rodriguez or Ernie Banks—the other came from Rico Petrocelli).

And if it turns out the comparisons of DeJong’s offensive profile to Randal Grichuk turn out to be accurate, there are worse things: an average defensive outfielder with Grichuk’s career 106 OPS+ is, well, Randal Grichuk, but at shortstop, it is a much more valuable player—so-so defensive shortstop Miguel Tejada had a 108 OPS+ for his career and he’s a six-time All-Star with an MVP award who is going to receive Hall of Fame votes.

DeJong is an intriguing prospect and his 2017 results suggest that even if his most likely long-term outcome isn’t spectacular, the error bars extend very far. He isn’t a mortal lock to be the starting shortstop for the 2018 Cardinals, and if a true superstar became available (think the Angels selling high on Andrelton Simmons, for instance), the Cardinals would be wise to consider that option. But DeJong will be a player worth monitoring, even with relatively steep regression seemingly inevitable.