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One Big Question: Can Jeisson Rosario add just a little bit of power?

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He can get by with a little, but not with none.

Boston Red Sox Spring Training Photo by Billie Weiss/Boston Red Sox/Getty Images

Welcome to the annual Over The Monster One Big Question season preview series. Over the next 40(ish) days, we will be running through every player on the 40-man roster and identifying a key question for them pertaining to the coming season. This should run us up to the start of the season, at least as it is scheduled now. We will go through the roster in alphabetical order. For the most part, these will run Monday through Friday every week running up to the week before Opening Day, though expect some weekend posts mixed in as well as the 40-man is expected to continue to be altered before the start of the season. You can catch up with every post by following this link. Today we take a look at Jeisson Rosario.

The Question: Can Jeisson Rosario bring a little bit of power into his game?

As has been well publicized both here and elsewhere, the Red Sox have been hard at work adding some depth to their farm system, with a significant number of their top prospects having entered the organization over the last 14 months or so. This essentially dates back to the Mookie Betts trade, and includes a pair of trades at the deadline last summer that look great for the team now. One of those was the Mitch Moreland deal that landed Hudson Potts, who we’ve covered in this series, as well as Jeisson Rosario, who we’ll cover today.

Rosario was signed by the Padres as a big J2 signing out of the Dominican Republic, gettin a $1.85 million bonus per Sox Prospects. He went right to the complex in Arizona in his first summer as a pro, and immediately started making an impact and turning heads with his athleticism and approach at the plate. He’d make his full-season debut in A-Ball as an 18-year-old in 2018, and was able to play all of 2019 at High-A before his 20th birthday. He spent last season at the Padres Alternate Site before the trade, and then finished things up in Pawtucket before being added to the 40-man this past winter to protect him from the Rule 5 Draft.

There are a lot of reasons to be excited about Rosario as a prospect. For one thing, he has had all of that aforementioned success despite the young ages. Despite being a teenager in all of his seasons in which he’s been able to play, he’s been above-average at the plate in each of them. And that largely comes down to phenomenal on-base skills that could make him a great leadoff option if the rest of the package comes together. In High-A in 2019 — again, as a 19-year-old — he drew walks at a ridiculous rate of almost 17 percent. In his three seasons as a pro, the lowest rate he’s carried has been a hair below 13 percent.

San Diego Padres v Diablos Rojos Photo by Hector Vivas/Getty Images

The defense is really the calling card here, though, as Rosario covers a ton of ground. He’s always been a great athlete, being known for his back flips in the outfield after victories, and he also has good instincts out in center field. There are some concerns about the athleticism from Instructs in the fall, and if that has fallen off that’s a big hit to his overall profile. I’m willing to wait to see what it looks like this summer before I worry too much about that, though.

Amid all of those very clear strengths in the scouting reports, the lack of power is about as glaring as it gets. Even if he maxes out the rest of his tools — and the hit tool projection at the highest end is more good than great — his lack of power is pretty much untenable in today’s game. Perhaps that will change with some of the alterations to the aesthetics to the game they are trying to make stick, but right now it’s just not the case.

Rosario is a center fielder, and while we don’t really consider that to be an offense-heavy position, you still need some power to make it work at that position. To look at just how much power was needed, I looked at the league-average center fielder’s Isolated Power and compared it to that of the league-average hitter regardless of position over each of the last five seasons. On average, center field was about eight points lower than the league-average hitter, and that gap has been shrinking over the last couple of seasons. Now, Rosario can probably live with a bit less power than that given his ability to draw walks, but he still needs more power than he’s shown.

And what has he shown? Well, almost nothing. Over his three seasons as a pro, the highest ISO he’s posted is just .080. Comparing major-league lines to minor-league lines is far from a perfect science so take any of this with the appropriate grain of salt, but it’s worth pointing out that over the last five seasons only three players have put up a league-average line (by wRC+) while carrying an ISO of no more than .080, minimum 250 plate appearances. Rosario’s defense could allow him to be a bit below average at the plate and still be a quality starter (hello Jackie Bradley Jr.), but it’s still not what you’re looking for in a prospect.

So now the question moves over to how likely is this to happen, and how does it occur. Unfortunately, the answer to the first question is not very likely. This has always been Rosario’s profile, and it’s unlikely to change. If he were to bulk up too much for more power, the losses in the field and on the bases would probably be too much to be worth it. One thing he can work on, though, is actually walking a bit less. Scouts have pointed to Rosario’s selectivity as part of the problem with his lack of hard contact, letting too many hittable pitches go by. It would not be the worst thing in the world to have Rosario go out for the first part of this season and not worry about walks. If it doesn’t work, you can scrap it, but it’s worth a shot.

I’m rooting for Rosario to figure it out, because athletic on-base-oriented players are very much my jam. And at the very least, if the athleticism drop-off from last fall wasn’t as bad as it seemed at the time, he should have a role as a bench player. An athletic outfielder who can get on base and play a good center field will be able to carve out some sort of career. But he’s obviously looking for more, and so are the Red Sox. Unfortunately, the way that happens is if he hits for even a little semblance of power, and that’s just something Rosario has never done.