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Magneuris Sierra is far from a finished product

His call-up was a lot of fun, but it was going to end one way or another.

Boston Red Sox v St Louis Cardinals Photo by Dilip Vishwanat/Getty Images

Let’s get one thing out of the way: Magneuris Sierra on the big league team was a lot of fun. He was only involved in seven games, but he made an impact. It never gets old to see a Cardinals prospect do that.

However, it does look like kind of a mirage. Sierra posted a 113 wRC+, good for 13% above-average. If he could sustain that, and combine it with above-average defense and base-running, he could easily be a 4-WAR player, which is an all-star level. Could he have continued to play that well? Some Cardinals fans are upset about Sierra being sent back down, but the answer is an emphatic “No”.

Remember throughout this article though, that there’s no shame in that. He started the year in High-A, and this is only his age 21 season. Few players reach the big leagues at that age, and with Sierra’s career going into the year, no one reasonably expected him to be ready to handle MLB pitching.

That he was called up in the first place has to do more with the minutia of MLB rules than his present abilities. Sierra had to be added to the 40-man roster last offseason or risk having him taken in the Rule 5 draft, like Allen Cordoba was. The team decided it was better to just go with Sierra for a few games rather than add someone like Harrison Bader to the 40-man before they had to. Bader probably isn’t ready for the show himself, but can at least say that he’s closer to Sierra.

Let’s look at a few plate discipline stats to start things off:

Magneuris Sierra Plate Discpline stats.txt

Player O-Swing% Z-Swing% Contact%
Player O-Swing% Z-Swing% Contact%
Sierra 33.3 % 68.6 % 67.9 %
Average 29.0 % 66.4 % 77.6 %

The contact rate is by far the most worrisome stat here. Among 399 players with 20 or more plate appearances, Sierra has the 35th lowest contact rate, inside the bottom 10%. His O-Swing% (rate that he chased pitches out of the zone) was higher than average, and his Z-Swing% (rate that he swung at pitches in the zone) was below average. It’s surprising he was able to sustain close to average K and BB rates, 21.9% and 6.3% respectively, but even those stats can be a victim of small sample size over the plate appearances we’re talking about.

If he had stayed in the majors, his plate discipline numbers indicate he probably would have trended the wrong way on both stats. The projections agree in terms of walk rate, as they would have expected it to drop to just 3.5% going forward. With average strikeout numbers, Sierra would need to do some damage when making contact to make up for that type of deficiency.

In his cup of coffee however, he failed to record a single extra base hit, not even one created by his speed. You can see why from his Radial Chart, based on the Statcast data hosted at

If you haven’t seen this type of graphic yet, I wrote about it twice before, once in regards to Aledmys Diaz’s contact quality issues, and once to show Stephen Piscotty might be poised for a breakout. Check out those (particularly the Diaz article) for a good explanation on what the image above means. Essentially, it shows every possible batted ball combination by Exit Velocity and Launch Angle, and the different colors form the six regions of contact quality that a batted ball can be. Each dot represents a batted ball for that player.

Magneuris “Barreled” zero batted balls. They’re by far the most productive batted ball. He also made “Solid Contact” on zero batted balls. That’s the second most productive batted ball. He does have several “Flares and Burners“, which are high-angle, low velocity batted balls or high-velocity grounders. These are similarly valuable to Solid Contact, but a little less so. They’re mostly flares though, and its easy to believe that bloopers might be a little less repeatable than other types of contact.

Here’s a chart breaking down the above image, and comparing it to average:

Magneuris Sierra Contact Quality Breakdown.txt

Player Barrels% Solid Contact% Flares and Burners% Under% Topped% Weak%
Player Barrels% Solid Contact% Flares and Burners% Under% Topped% Weak%
Avg wOBA 1.433 .692 .630 .095 .206 .460
Lg Avg 5.6% 5.1% 25.3% 24.1% 36.1% 3.8%
Magneuris Sierra 0.0% 0.0% 34.8% 17.4% 43.5% 4.3%

Zero barrels and Solid Contact leaves quite a hole in his contact profile. He also “tops” the ball at a well-above average rate. He hits an above-average amount of Flares and Burners as well as “Hits Under” the ball a below-average amount of the time, but it’s not enough to make up for it.

Using Baseball Savants’ xwOBA stat, which adjusts the on-contact portion of a player’s wOBA based on the Statcast data, we see that Sierra should have had much worse results. His wOBA in his time with the big league club was .353, but his xwOBA was just .288. That’s 285th out of 423 players with at least 20 plate appearances, or placing in about the bottom third of the league. The difference between his xwOBA and wOBA makes for the 35th biggest negative difference, inside the bottom 9%.

From eyeballing the leaderboards, his xwOBA translates to about a 75 wRC+, or 25% worse than average. Only 28 of the 188 qualified players have a wRC+ that low. This is mostly the result of a weak ability to generate Exit Velocity. Among 401 hitters with at least 20 batted balls, he ranks 16th worst in average EV.

xwOBA doesn’t take into account speed, and Magneuris has wheels that should give him more infield hits than average. He has, with 2 infield hits on 9 grounders fielded on the infield, giving him a 22.2 IFH% (infield hit percentage). Is that sustainable? Absolutely not. Since 2014, Chris Young leads qualified players in IFH%, at just 14.3%. It’s a nice part of his profile, but it’s not going to carry him with the problems that exist. The fact that he’s fast doesn’t justify the ridiculously high .478 BABIP, which is the only real positive about his results.

Of course, this is all small sample size. However, the only reason to believe Sierra might actually be ready for the majors would be this short cup of coffee. Being slightly above average at Full-season A and High-A doesn’t really translate to being ready for the majors. The underlying stats at the major league level confirms that assumption, contrary to the results in his time in St. Louis.

Even with all of these red flags, Sierra still improved his outlook. At the beginning of the season, the projections saw him as a 60 wRC+ hitter at the major league level, and now he’s pulled that up to a 62. 15 points of wRC+ correspond to 1 win over the course of a full season though, so even with the base-running and defense, he likely isn’t even a replacement level player yet.

Again, that’s not really a problem, because no one should have expected him to be an actual quality MLB player already. The Cardinals see him as improved, assigning him to Double-A rather than High-A where he started the year. While he might be back in September to serve as a base-running and defensive specialist, until then he deserves everyday playing time to see if the bat comes around. It doesn’t need to come around all that much for him to be valuable when considering his defense and base-running. It’s probably not going to come around at all though if he doesn’t get to play everyday and maximize his development.

In Double-A, he’ll be getting everyday playing time. Maybe they send him to the Arizona Fall League at the end of the year, or perhaps Winter Ball to get everyday reps. We won’t get to see it - unless you subscribe to - but it’s what’s best for the prospect and the Cardinals. It was a fun ride, but had he stayed, it probably wouldn’t have ended pretty.