One Big Question: Will Jeisson Rosario’s plate discipline buy him another year on the roster?

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 Boston Red Sox 40-man roster and identifying a key question for them pertaining to the coming season. 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, at least as things are scheduled right now. Obviously, the lockout may change the timing of the season, and it also means we will likely see more additions of new faces. If need be, we will add some weekend posts to fit any and all additions to the 40-man before Opening Day. You can catch up with every post by following this link. With that, today we cover Jeisson Rosario.

The Question: Will Jeisson Rosario’s plate discipline buy him another year on the roster?

The lost 2020 season in the minor leagues had such a wide range of effects on minor league players. With everyone stuck in place for a long period of time, training away from their team, and then finally returning to Alternate Sites and fall leagues, not one player had the same training regiment as the next. Even in 2021, minor league seasons did not start until May, and opponents were limited to intra-division play based on geography. For a player like Jeisson Rosario, add in a trade from one Alternate Site to another and your growth as a player is even more stunted.

The Red Sox received Rosario, along with Hudson Potts, from San Diego at the 2020 trade deadline in return for first baseman Mitch Moreland. By the time true competitive action began again, Rosario had gone from a 19-year-old continuing his ascent up the minor league system in Southern California (High-A Lake Elsinore Storm) to the exact opposite corner of the Lower 48, as a 21-year-old with the Double-A Sea Dogs in Portland, Maine.

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While Rosario’s power is virtually zero (he has not hit more than three home runs at any level), his plate discipline has has been one of the reasons he’s remained on the prospect radar throughout the years. For example, his .242 average at High-A in 2019 becomes a lot more palatable alongside a .372 OBP, thanks to a 16.6 percent walk rate and a 21.7 percent strikeout rate. Rosario’s wRC+ was 102 in that season and stayed above 100 (the league and park-adjusted average) at each level he had played. Alongside some speed, both on the bases and in the outfield, (though reports indicate the speed which was once a weapon is now just fine) and a decent arm, there was a path to a bench outfielder or better that may even be able to hit atop the order in a pinch thanks to the plate discipline.

Unfortunately, things seemed to go in the wrong direction across the board in 2021 for Rosario, as he attempted Double-A for the first time at the age of 21 instead of age 20, as was anticipated.

Jeisson Rosario | Fangraphs

The most glaring change is the significant increase in strikeout rate, but Rosario’s ground ball rate also continued to increase from 48.6% at Low-A, to 50.0% at High-A, to 51.5% at Double-A. The slap approach was even more pronounced against left-handers in 2021, hitting the ball on the ground 55% of the time (compared to 48% against RHP) but also striking out 29.3% of the time (compared to 27.6% vs RHP). As Eric Longenhagen noted prior to the start of last season, “Rosario is also very tough to get to swing-and-miss in the zone, but some of that is because he’s very conservatively poking, slapping, and slashing soft contact all over the infield and not really trying to hit for power.” Numerous scouting reports have recently put Rosario’s speed closer to average and he was only 11-for-18 stealing bases in 2021.

All of this adds up to even slimmer margin for error with Rosario, who will need his plate discipline, both with a high walk rate and a reasonable strikeout rate, to keep him on the 40-man roster. It isn’t out of the question for him to make improvements with the bat to get to a .240-.250 average in the higher levels of the minors with a .370-.380 OBP, but the strikeout rate will certainly need to get back to the 20% range that he sported in the lower minors. Again, with a lost 2020 and choppy 2021, Rosario needs a smooth 2022 to get back on track. Unfortunately, he can’t catch a break and as a member of the 40-man roster, Rosario is unable to report to spring training with his fellow minor leaguers and is falling further behind by the day.

Rosario, along with Hudson Potts, came over in the Mitch Moreland deadline deal of 2020 and while it could be seen as frustrating to see them both waived and taken off the 40-man, the expectations couldn’t have been too high for the Moreland return. Fortunately, numerous Chaim Bloom moves from the second half of 2020 have more than exceeded the expected return.

With numerous free-agent signings likely on the horizon after the completion of the lockout, there will be some players placed on waivers in a corresponding move, as Matt referenced with Potts yesterday. Rosario is certainly a candidate to be on the list of players that could be waived and not come back to haunt the Red Sox in the long term. In an ideal world, it would be great to get the 22-year-old Rosario one more year in the system to make strides and prove he could at least be a bench bat in the major leagues someday.