Magneuris Sierra and ultra-young Cardinals rookies

When the Disabled List stints of Stephen Piscotty and Jose Martinez required the St. Louis Cardinals to promote two outfielders from the minor leagues, one of the choices was obvious. Tommy Pham, a versatile 29 year-old with MLB experience and the ability to play all three outfield positions, was an automatic.

Harrison Bader, the organization's most ballyhooed outfield prospect, made sense. While Bader, who turns 23 next month, was not an ideal choice (the ideal choice, of course, was "nobody gets hurt and maybe the Cardinals acquire Mike Trout and Bryce Harper just to be safe"), he seemed to be the safest of the options available. But instead, the Cardinals promoted high-A center fielder Magneuris Sierra to St. Louis.

Sierra's ascent to the big leagues was a surprise, but he has been a tremendous success during his cup of coffee. In his first 26 plate appearances, Sierra has reached base eleven times--via nine singles and two walks. He has scored seven runs, more than three position players who have spent all of 2017 on the active roster (Matt Adams, Eric Fryer, Greg Garcia). While he has yet to steal a base, compared to two outs which he has made on the bases, FanGraphs lists Magneuris Sierra as a plus base runner so far, and indeed, video evidence seems to back up this hypothesis.

Defensively, Sierra has not played enough—just fifty-nine Major League innings—for his statistics to provide a significant glimpse into his true talent, but early returns look decent. His aforementioned speed, a critical skill particularly for center field, manifested in this fairly routine looking play which, per Statcast, is only caught 35% of the time.

Magneuris Sierra’s time in the big leagues has been a pleasant surprise, and there are two ways to evaluate it (there are probably way more than two ways to evaluate it). We could look at the unlikelihood that Sierra maintains what he has done so far, noting that he has yet to manage an extra-base hit despite his speed and that while he has an impressive .375 batting average, this has come with the assistance of an unsustainable .450 batting average on balls in play. We could note that Sierra has only once surpassed his current wRC+ in the minor leagues once, in 2014, and had a wRC+ of 113 in Palm Beach this year.

But most fans know this. Most fans realize and understand that while Magnerius Sierra is an exciting player who possesses some of the skills necessary to become a very good MLB player, he is probably not a long-term big leaguer in his current state. As soon as Stephen Piscotty is available to return, Sierra will likely be sent back to the minors until at least September call-ups.

Instead, rather than forecasting what Magneuris Sierra will do, let’s appreciate what he has already done. Because, particularly in the modern era, it is a rarity.

Magneuris Sierra was born on April 7, 1996. Wanna feel old? Here was the #1 song in the United States the day that Magneuris Sierra was born.

Last season, Alex Reyes was hyped immensely for debuting at such a young age—21 years, 11 months, and 11 days. Sierra made his MLB debut at 21 years, 1 month. He is the youngest player on the St. Louis Cardinals since 1999, when Rick Ankiel made his MLB debut at 20 years, 1 month, and 4 days.

Sierra already ranks fifth among St. Louis Cardinals in the 21st century by plate appearances by a player in his age 21 or under season.

1. Albert Pujols, 676 plate appearances (2001)
2. Yadier Molina, 151 plate appearances (2004)
3. Rick Ankiel, 83 plate appearances (2000-2001, 94 PA counting his 1999 appearances)
4. Bud Smith, 28 plate appearances (2001)
5. Magneuris Sierra, 26 plate appearances (2017)

Despite Sierra’s limited track record—while his performance has been very good so far, this works out to 0.2 FanGraphs Wins Above Replacement because, well, twenty-six plate appearances. But only seven players surpassed this at age 21 or younger: Pujols (2001 Albert Pujols was by far the gold standard in the 2000s by this measure), Molina, Ankiel, 2016 Alex Reyes, Bud Smith, 2012 Shelby Miller, and 2013 Carlos Martinez.

As the preceding list indicates, young position players tend to be less common than young pitchers, but still, in Major League Baseball in the 21st century, 134 players have reached Sierra’s plate appearance total. And of those 134 players, Sierra has the highest batting average. He has the third highest on-base percentage, behind #2 Corey Seager and #1 (go figure) Daric Barton. And despite an isolated power of .000, reflecting his complete lack of extra base hits, he has a higher OPS than such notables as Freddie Freeman, Prince Fielder, Manny Machado, and Troy Tulowitzki.

In Sierra’s third game in the Majors, on May 9, he went 2 for 4 with two runs scored. His Win Probability Added for the game was 0.142, reflecting his success in high leverage situations in a game which the Cardinals eventually won by one run over the Miami Marlins. Only three Cardinals in the last twenty seasons exceeded this mark in his first three career games: Jarrett Hoffpauir in 2009, and Aledmys Diaz and Jeremy Hazelbaker in 2016.

No player younger than Magneuris Sierra (at the time of the game) has scored more runs in a game so early in his career this decade. And only two men younger than Sierra, San Diego Padres catcher Luis Torrens (whose wRC+ presently stands at -36, and to be clear, that’s a negative sign and not a hyphen) and Los Angeles Dodgers pitcher Julio Urias, have ever played Major League Baseball.

Magneuris Sierra, again, will probably be back in the minor leagues soon. And while he has shown tons of promise, and I look forward to tracking his progress, nothing is guaranteed. He might develop extra-base power in the next year; he might pull a Joe Nuxhall, returning to the bigs nearly a decade after his debut for good; he might remain in the minors. But he has already had an electric and memorable, albeit to this point extremely brief, Major League career.