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Yoan Moncada struck out six times in his first 14 plate appearances in the big leagues.
Yoan Moncada struck out six times in his first 14 plate appearances in the big leagues. Ben Margot/Associated Press

There is immense promise in what Yoan Moncada has done already. In his first four big league games, the 21-year-old is 4-for-13 with a double, good for a .308/.357/.385 line, and he’s shown tremendous arm strength along with the pure athleticism that could translate to an impressive defensive fit for the position once he gains greater familiarity there.

Yet as Nick Cafardo writes, he’s also still very much a work in progress, and in this case, there’s also a bit of a red flag related to his rough edges. Moncada punched out in all three of his plate appearances against Edwin Jackson on Monday, and he now has fanned six times in his first 14 plate appearances in the big leagues.

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“They threw some breaking balls down under his swing and there was some swing and miss there,” said Red Sox manager John Farrell. “The scouting reports will get out and he’ll be forced to make some adjustments. . . . The breaking ball is going to be something he’s going to have to contend with.”

When the Sox promoted Moncada from Double A Portland, they committed to a two-level jump for a player who had struck out in 30.9 percent of his plate appearances in Portland. While Farrell said prior to Moncada’s promotion that he represented the sort of talent that made him a “direct comparison” to Xander Bogaerts, his strikeout total suggests otherwise.

Indeed, of all of the most prominent Red Sox prospects called up in the last five seasons who had fewer than 100 games in Triple A (thus excluding Travis Shaw and Brock Holt, who had considerably more upper levels experience than other callups), dating to Will Middlebrooks’ early-season summons in 2012, Moncada’s strikeout rate stands out as far and away the highest.

Strikeout rates for recent Red Sox prospects
Player Year Level preceding callup K rate at that level Majors K rate in debut season K rate increase in majors
Yoan Moncada 2016 Double A (45 games) 30.9 42.9 39%
Andrew Benintendi 2016 Double A (63 games) 11.4 23 102%
Blake Swihart 2015 Triple A (38 games) 19.2 24.9 30%
Mookie Betts 2014 Triple A (23 games) 12.3 14.6 19%
Christian Vazquez 2014 Triple A (67 games) 19.3 16.4 -15%
Jackie Bradley Jr. 2013 Double A (61 games) 18.1 29 60%
Xander Bogaerts 2013 Triple A (60 games) 17.2 26 51%
Will Middlebrooks 2012 Triple A (40 games) 22.5 24.5 9%
SOURCE: Baseball-Reference.com

The switch-hitter is the only member of the group who posted a strikeout rate in excess of 30 percent at his last minor league level before his callup. Indeed, of the other seven members of this callup group, only one (Middlebrooks, 22.5 percent) had a strikeout rate that exceeded 20 percent.

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When Bogaerts was called up in 2013, for instance, he’d struck out in 19.7 percent of his plate appearances in Double A, then trimmed that number to a 17.2 percent rate in Triple A prior to his big league callup. In his first exposure to the big leagues in August and September of 2013, Bogaerts then saw his strikeout rate jump by about 50 percent.

Every Red Sox callup of the last five years except Vazquez has seen his strikeout rate go up in his first big league season. If that form holds, that means that Moncada is likely to whiff in at least one out of every three big league plate appearances this month.

It’s not impossible to be a very good player while striking out with that kind of frequency (though typically it requires a player to possess exceptional power, like Chris Davis or Miguel Sano).

But it is challenging, and suggests a potential vulnerability for now that opposing pitchers will seek to exploit.

Moncada proved a quick learner in his minor league career, taking huge strides in short periods of time. That past is part of the reason why his strikeout rate didn’t hammer his prospect status. Sox officials believe that there will be another breakthrough on the horizon when it comes to Moncada’s ability to manage his strikeouts.

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“He still swings and misses a lot, but at the same time, he’s taking good swings. He’s a work in progress. He needs to stay up the middle of the field a little bit more, but when he makes contact, it’s impressive,” Portland manager Carlos Febles explained last week. “Once he learns his swing and is consistent with his approach, I believe he will be pretty good. He’s not at that point yet. He’s not far off at this point. He just needs to continue. … He doesn’t need to hit for power. His game is speed. This guy is fast. Once he realizes he needs to put the ball in play and run, he can be a .330 hitter with 20-25 homers.”

For now, however, he’s not that hitter, which in turn raises an interesting question posed by Rob Bradford of WEEI.com: Did the Red Sox put the cart before the horse in declaring Moncada their regular third baseman against righthanded pitchers, rather than taking the more measured approach that they struck when Bogaerts debuted?

That remains to be seen. There’s a chance that, as many prospects with swing-and-miss vulnerability have done, he could excel in his initial glimpse of the big leagues, in the process giving the Sox a considerable boost to their postseason chances. Still, at some point, there’s likely to come a point where Moncada will endure a transitional struggle, in a way that offers a reminder that despite his enormous ceiling, his development remains incomplete.

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Peter Abraham of the Globe staff in San Diego contributed to this report. Alex Speier can be reached at alex.speier@globe.com. Follow him Twitter@alexspeier.