Who will play center field in 2018?

On Sunday, the red baron evaluated the outfield depth of the St. Louis Cardinals, noting that Tyler O’Neill, acquired from the Seattle Mariners in July for Marco Gonzales, has joined an already-impressive list of potential impact outfielders for the Cardinals over the next few years. By September of 2018, he suggests (and he knows far more about prospects than I do) that the Cardinals may have nine MLB-caliber outfielders. Even if this is a bit optimistic, having even six or seven seems like overkill.

Barring a trade (or the surprise non-tendering of a lifetime), the last two regular starting center fielders for the Cardinals will be available to the Cardinals in 2018. Dexter Fowler was signed after 2016 to solidify center field, but while his offense has been more or less as advertised, he has struggled to stay healthy and his defense, which had been statistically solid over the previous two seasons, has fallen back to the below-average level at which he had performed prior to 2015. Randal Grichuk was moved to regular duty in left field before the 2017 season, but he has been average-ish by Ultimate Zone Rating at center field in his career and there is little reason to believe that his true defensive talent has plummeted substantially in the year since his position shift.

Fowler and Grichuk are reasonable candidates to play center field for a Major League team, as each has done so in the recent past. But new candidates have emerged in 2017. Most notable is Tommy Pham, the Opening Day right fielder for the Memphis Redbirds, who became a five-plus Wins Above Replacement player upon his promotion to St. Louis and whom general manager Michael Girsch said on Tuesday had been penciled into the 2018 everyday lineup. While Pham has made his share of starts in center field, a majority of his starts with St. Louis have been in left field, while Dexter Fowler started in center field.

Fowler and Pham, as the red baron referenced, seem mostly assured of a starting spot somewhere in the outfield in 2018. Pham has been the best player on the Cardinals this season, and while Fowler has perhaps been a minor disappointment (his offense has been very good, but his defense and durability have left some to be desired), he has hit far too well to imagine the Cardinals justifying putting their $16.5 million per season outfielder on the bench when healthy.

Since both have been trusted to play center field, it seems like an obvious choice that one will handle the majority of the innings there in 2018. But as referenced earlier, the first-choice center fielder (Fowler) has been a defensive liability in 2017. Yes, small sample sizes, and yes, his previous two seasons were average, but Fowler had a long track record of being a sub-par defensive center fielder. Although Dexter Fowler is still a reasonably fast player—per Statcast, his top sprint speed of 28.2 feet per second is the median for MLB center fielders—he has taken a step back from previous seasons (he peaked at 28.6 ft/sec in 2015 and 28.8 ft/sec in 2016) and has a history, including this season, of foot and knee injuries.

Tommy Pham has been above-average by UZR in 2017, as he was in 2015, but in 2016, Pham was quite a bit below-average, particularly in center field, where he logged 239 innings. It’s not a huge sample, but he was poor enough that Pham’s career center field UZR is slightly below-average. Could his problems with the degenerative eye condition keratoconus have caused him to decline defensively beyond what his other raw physical skills would suggest? Perhaps, but Pham still stands at just 754 career innings in center field, a total exceeded by twenty-one center fielders in 2017, including Dexter Fowler.

The fastest prospective center fielder on the Cardinals’ 40-man roster, or with any reasonable chance of logging playing time in the outfield, is Magneuris Sierra, whose ft/sec rate of 29.9 is tied for third in MLB in 2017 with Cleveland Indians center fielder Bradley Zimmer, with the two trailing only Byron Buxton of the Minnesota Twins and Billy Hamilton of the Cincinnati Reds. And Sierra managed this with far fewer opportunities than the other three to reach his peak.

Statistically, in a microscopic sample, Sierra has been below-average in the outfield (though slightly above-average in center field), but he has not played nearly enough to take these numbers too seriously. The eye test suggests that Sierra’s speed should more than compensate for any lack of refinement he may have.

But while fans ought not worry about his ability to handle the position—I believe he is the best defensive center fielder in the organization—fans should be concerned about Sierra’s bat: his 99 wRC+ is more than acceptable for a premium defensive center fielder (this is essentially what Kevin Kiermaier was with the Rays in 2015, a year in which he was an MVP candidate), but Sierra managed to reach an ever-so-slightly-below-average clip with a .432 batting average on balls in play.

While Sierra is fast enough to beat out some infield ground balls, of the 480 batters with at least 40 batted ball events in 2017, he ranks 441st in average exit velocity (and most of the players behind him are pitchers). No position player in baseball has had a lower percentage of batted balls with an exit velocity over 95 MPH. Sierra has a .000 isolated power, and his minor league track record suggests his true power talent isn’t far above that. Mike Matheny was unwilling to give substantial playing time in center field to Peter Bourjos, an elite fielder and a so-so bat who was nevertheless light-years ahead of Sierra’s current level at the plate. It’s nearly impossible to imagine Matheny regularly penciling Sierra into the lineup.

Assuming still that Pham and Fowler are outfield shoo-ins, the other likely candidates for center field are unlikely to jump into center field. Randal Grichuk has been trusted to play center field, but again, he was mostly avoided there this season. Stephen Piscotty played center field sometimes in 2016, but this was in order to accommodate Matt Holliday and Brandon Moss, and Piscotty was the lesser of three evils in an arrangement designed to maximize offense. And if Jose Martinez cracked the lineup (and his offense has been strong enough in 2017 that expecting him to retain at least some of his magic in 2018 isn’t completely absurd), it wouldn’t make sense to suddenly try him in center field in lieu of the actual center fielders also on the field.

If the Cardinals want an elite defensive center fielder whom they could justify starting regularly, they’d probably have to make a trade. The only upcoming free agent who fits this description, Kansas City Royals center fielder Lorenzo Cain, will be: 1. Very expensive; 2. Nearly 32 years old and seemingly susceptible to declines in speed and overall defensive quality; 3. Therefore further blocking the MLB-caliber depth the Cardinals have. The ultimate fantasy is that the Cardinals could package outfield prospects for a center fielder (say Kiermaier, Michael Taylor, or Jackie Bradley Jr.), but this would require a team to want to inherit the Cardinals’ semi-problem of too many prospects and not enough playing time.

The path of least resistance for the Cardinals would be to keep Dexter Fowler in center field, because he seems to really want to play in center field. It seems weird that a Major League Baseball team would honor the same approach my little sister used to sit in the front seat when we were growing up, but this would cause the least ruffling of feathers. Perhaps the Cardinals believe that Pham has a greater comparative advantage in left field than in center field, but if it is indeed a matter of keeping players happy, it is understandable but also a bit worrisome long-term, because it is inevitable that at some point, somebody will definitively pass Dexter Fowler on the center field depth chart.