What is Magneuris Sierra?

In a St. Louis Cardinals season which could often be described as bland, a boring compilation of average-ish players having average-ish individual seasons, leading to an average-ish 83-79 record and, appropriately, a spot in the middle of the National League Central standings, genuinely exciting players felt even more dynamic than they might have in previous years.

The best player on the Cardinals by any reasonable measure in 2017 was Tommy Pham, and he certainly met the criteria of excitement. I say “certainly” as though excitement isn’t a subjective quality, but how else can one describe a player who began the season in the minors and had just 358 MLB plate appearances to his name entering 2017 who nevertheless reached the vaunted .300/.400/.500 AVG/OBP/SLG plateau and stole more bases than any Cardinal since Tony Womack in 2004?

Pham was exciting, but he was also extremely productive. The former was great, but the latter was ultimately what assured that he will be a part of the team’s plans in 2018 (barring a, like, Literally The Angels Are Offering Mike Trout Trade). And only one position player was even in the same stratosphere as Pham in 2017 for excitement, albeit in much less playing time—21 year-old outfielder Magneuris Sierra.

Entering 2017, Sierra was a known prospect, though not exactly considered a blue-chip one. Viva El Birdos prospect guru Aaron Schafer ranked Sierra 15th in the Cardinals system, and while some outlets had him higher, he was not generally heralded as a future superstar. The word commonly used to describe Sierra was “raw”—his speed was ample and by extension, his future as a defensively adept center fielder seemed assured.

But at the plate, Sierra did not appear to be MLB-ready. In 2016, Sierra was 15% above-average in A-ball by wRC+. And this was with a very high .367 batting average on balls in play (in Sierra’s defense, exceptionally fast players tend to have naturally higher BABIPs, though .367 is higher than one could reasonably expect of anybody)—his .088 isolated power, with just three home runs in 562 plate appearances, suggest a player dependent on luck to survive offensively.

But after Sierra was surprisingly promoted from high-A in May, he went on a tear. In May, over his first seven games, Sierra had a .367 batting average. And for a fan base that worshiped speedsters such as Vince Coleman and Willie McGee in the 1980s, Magneuris Sierra represented a refreshing throwback. Firmly aware that Sierra wasn’t actually going to finish his career with the highest batting average in MLB history, I decided to try living in the moment.

So far, what I’ve written is about what Sierra was, though, and while what he was made for an interesting story, what ultimately matters now for the Cardinals is what he is and what he will be.

Not considering past performance when evaluating future performance, of course, doesn’t make much sense, either. The “stats vs. scouts” debate never really existed, and every organization in baseball has valued both forever (while each “side” has become far more sophisticated over the years). So what is Magneuris Sierra?

As a base runner

The most obvious element of Magneuris Sierra’s game is speed. By sprint speed, Sierra trailed only Byron Buxton and Billy Hamilton, and while the measurement does not require sustained success and thus a player such as Sierra with far fewer opportunities can compete, it is clearly advantageous to have more opportunities to max out one’s peak speed. Buxton and Hamilton were each measured over 50 times—Sierra was measured fewer than 10 times.

Despite this, Sierra was not nearly the base thief one might expect at the MLB level. Although he reached first base 23 times, Sierra attempted four steals, only two of which were successful. In the minors, he stole bases at a higher volume, but has had problems getting caught. In 2016, he stole 31 bases but was caught 17 times. In the minors in 2017, Sierra was caught 10 times while successful 20 times, succeeding at exactly the two-thirds rate generally considered the break-even point for stealing bases.

But despite his MLB shortcomings in steal efficiency, FanGraphs measured him as solidly above-average as a whole, counting not only steal attempts but taking extra bases, tagging up, and such often overlooked elements of the game. This is in a microscopic sample size, but Sierra also generally appeared to be a fine runner.

As a fielder

Magneuris Sierra was a below-average fielder with the St. Louis Cardinals by Ultimate Zone Rating. Given his reputation, this seems impossible, but he was.

But this is more a reflection on the metrics than on Sierra. The numbers do not lie as much as they deceive—a player who goes 2-for-5 with a home run is not actually a .400 hitter who is on pace to hit 162 home runs in a season, and a player who botches one play is not an incompetent buffoon incapable of handling the position whatsoever.

Easily Sierra’s most disastrous outfield spot by UZR was left field, and according to Inside Edge Fielding, he successfully converted a routine (90%-100% chance) play, he did not convert an impossible (0%) play, and he did not convert a likely (60%-90%) play. That one play made all the difference. In right field, where he was also rated as below-average, he had one play not rated as routine or impossible (a remote, 1-10%, play, which he did not convert), and this cost him. And in center field, usually considered the most difficult of the positions, he was above-average.

Scouting suggests that Sierra has potential to be a great fielder, and while he may not have been perfect at the big-league level in 2017, a grand total of 137 ¹⁄₃ innings are hardly enough to justify dramatically changing one’s opinion. He may not actually become a Gold Glove winner in center field, but the potential remains.

At the plate

In 2017, with the St. Louis Cardinals, Sierra made 64 plate appearances, and he posted a final BABIP of .413. In 1977, Rod Carew posted a BABIP of .408 for the Minnesota Twins, and this is the highest mark by a qualified player since 1924. Magneuris Sierra may be a high BABIP player, but he isn’t going to be a .413 BABIP player.

But even if he were, his 2017 wRC+ stood at 86. This would put him on par with San Francisco Giants shortstop Brandon Crawford, which feels appropriate—Crawford is a very good defensive player and thus, even in a season in which his offense lacked, he was still roughly a league-average player. And Sierra could be that if he maintains his .413 BABIP. Which he can’t.

By xwOBA, which measures a player’s expected hitting production based on batted-ball data, Sierra’s expected wOBA was .248, tied for 465th among the 525 players with 50 or more at-bats in 2017. Most of the names below him are pitchers. The lowest wOBA in 2017 among qualified hitters was a tie between Royals Alcides Escobar and Alex Gordon, at .269.

Last Tuesday, I advocated for the Cardinals to sign Jarrod Dyson, who is a below-average hitter who is very good at defense and base running. Some agreed, but many others expressed the belief that the Cardinals already had a Jarrod Dyson type in Magneuris Sierra. But the problem with Sierra as he currently stands isn’t that he is, like Dyson, a below-average hitter—it’s that he’s an abysmal hitter.

But he has skills. Undeniably, Magneuris Sierra has skills. And he can develop into a Jarrod Dyson type of player—he’s probably not going to become a prodigious slugger (his MLB ISO of .000 doesn’t inspire confidence, at least) but if he can develop at least an adequate bat in the minors, he could factor into the Cardinals’ future. But he’s too much of an uncertainty for the Cardinals to build around him or refuse to consider him as a piece to acquire talent that is certain to be MLB-capable.