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Projecting the Mariners’ return for James Paxton

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Many said that the Mariners received a “light” return. Is that truly the case?

Boston Red Sox v New York Yankees Photo by Mike Stobe/Getty Images

The Mariners and Yankees made headlines earlier this week when the two clubs sent James Paxton to New York for a trio of prospects.

The move was the first major transaction of the offseason, and it is the first of the Mariners’ rebuilding — or, maybe, retooling — phase, which was long rumored as a possibility to come this winter.

Much has been made of the Yankees’ acquisition of Paxton, but there is not a lot on the Mariners’ overall return. I’m here to change that.

Justus Sheffield

Sheffield is the headliner in the Mariners’ return package and rightfully so.

For a left-handed pitcher, Sheffield’s fastball, with its ability to reach 98 mph, is certainly exciting. But he also adds a slider, which also rated out as a 60 (above-average) on the 20-80 scale in MLB Pipeline’s scouting report. His changeup also has the ability to miss bats, and this three pitch mix could give him the upside of being a No. 3 starter.

Sheffield’s biggest concern, however, is his control. He walked 10.5 percent of the batters he faced across Double-A and Triple-A with the Yankees last year, even after walking just 7.4 percent the year prior. (The MLB-average walk rate for a pitcher is 8.5 percent.) The strikeouts have always been there. Sheffield has been praised for his ability to mix his pitches, and this has kept batters off balance, resulting in a strikeout rate upwards of 25 percent in 2018.

FanGraphs pegs Sheffield as a 50 (average) on their report, which roughly correlates to a 2-WAR peak player. Looking at Steamer projections, Sheffield could be worth about 0.6 wins this year. Taking from the rough WAR progression system on the FanGraphs Contract Estimation Tool, Sheffield projects in the ballpark of 7.1 WAR over his first six years in the big leagues, which is far from being a non-factor in the Mariners’ future plans.

A 7.1 WAR6 for Sheffield sounds about right, considering his “peak” WAR in this scenario is 1.6, close to what a 50 future value player may produce. Paxton, in comparison, projects to be worth about 7.5 WAR over the next two years, the time that the Mariners would control him. So, in theory, a Sheffield who meets projections could almost make up for the loss of Paxton himself, while also potentially serving in an important role on the next contending Mariners team.

Erik Swanson

The right-handed pitching Swanson is mostly a two-pitch pitcher, relying on a fastball that can touch 98 and a solid slider. He could end up as a backend starting pitcher, but it’s more likely that he would be a middle inning reliever for a contender.

Swanson mainly started across three levels in the minors last season, reaching as high as Triple-A. But he’ll be 25 next year, so the potential for upside is limited. In Kiley McDaniel’s piece at FanGraphs from Nov. 20, Swanson is a 40 on the 20-80 scale for future value, with an approximate 1.0 WAR peak.

With this knowledge, we can attempt to project Swanson’s first six years in the Major Leagues. Using the aging curve system with regards to his age and a Steamer projection that has him at 0.3 wins in 2019, Swanson projects to be worth about 4.1 WAR in these six years, again a welcome sight to a Mariners organization that likely only traded away 10-12 wins in current value.

Dom Thompson-Williams

Thompson-Williams is the question mark in all of this. He is 23, yet he only reached High-A Tampa last year. McDaniel proposes that Thompson-Williams could have everyday outfielder upside if he continues to hit as he did last year (.909 OPS in 415 plate appearances) and moves quickly through the minors. But it’s unreasonable to expect him to become a regular Major Leaguer before he turns 26, with an outside chance that he makes it there in his age-25 season in 2020.

With that said, Thompson-Williams probably won’t end up as anything more than a bench bat for Seattle, also equating to a 40 in future value.

We have just limited knowledge on Thompson-Williams’ future, so it’s hard to completely project what he’d be worth in terms of total wins. If he got regular at bats in the Majors right now, Thompson-Williams projects to be a -0.6 win player, per Steamer. Assigning the aging curve to Thompson-Williams’ current -0.6 WAR projection, he’d be worth about a half-win over his time in the Majors, assuming he gets his first full big league season at age-26. That might be a bit harsh, but because Thompson-Williams is such an unknown, it’s hard to know what he’ll ultimately become in Seattle.

The overall value

Adding across all three players, I calculate the Mariners’ total value acquired in this trade to be worth about 11.7 total WAR. As mentioned above, Paxton alone could be worth somewhere in the ballpark of 7.5 WAR, using the aging curve progression. That would result in a net positive for the Mariners, suggesting that this trade isn’t as one-sided for New York as many originally thought.

Of course, Paxton’s 7.5 WAR over the next two years might be too light of a projection. After all, he was worth 8.4 WAR over the previous two years. A lot depends on his health, which almost certainly played a role in the quality of the Mariners’ return here. Had Paxton been completely healthy last season, his value would have been much higher. But a 160 13 innings pitched season, representing a career-high for Paxton, means otherwise.

Seattle is banking on Sheffield meeting his 50 future value projection or Paxton not staying healthy. In either of those cases, the Mariners could actually win this trade when we look back upon it at some unknown date in the future.


Devan Fink is a Featured Writer for Beyond The Box Score. You can follow him on Twitter @DevanFink.