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Mariners 2021 Free Agent Target: Marcus Semien

Some greenbacks could could move the longtime A’s shortstop from Kelly Green to Northwest Green.

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Oakland Athletics v Seattle Mariners Photo by Rob Leiter/MLB Photos via Getty Images

Upgrading the Mariners roster this winter is an exercise in short and long term prioritization. The nature of the current free agent structure is such that players rarely reach free agency before they’re into their 30s, with their best days of performance on their resume but not as reliable to sustain going forward. Younger free agents, even those who have just hit age-30, are prized as a result, as possible targets for long-term deals that work well for player and team alike. For the Mariners, who want to begin contending again and hope to have cultivated the depth for a more perpetually In It roster after their multi-year reset, a younger upgrade who fills a hole of lesser organizational talent is an ideal add. That could well be longtime rival Marcus Semien.

Semien has been a decent player, but who he is going forward is a matter of faith. His offensive spike in 2019 make him the player in free agency with the best single season (by fWAR) of any player on the market, but he’s a polarizing target thanks to a few questions.

  1. Which hitter will teams get going forward?
  2. What is his defensive home?
  3. Will his profile age well enough?

Craig Edwards at FanGraphs wrote on the potential for Semien to be overlooked this winter, and I think there’s a lot to his argument. Much of my case for Semien is summarized in Edwards’ piece, so I recommend following the link, but the biggest takeaway highlighted is how different Semien’s 2020 line would look if the roughly 1/3rd of a full season also included his exceptional playoff numbers to add to the sample by seven games. From Edwards:

The uncertainty on defense carries over to offense as well, given his career prior to 2019 and his batting line in ’20. As mentioned in our rankings, Semien’s 2020 line suffered because of a two-week slump at the beginning of the season, and because his playoff numbers aren’t included in his final line. An extra 30 plate appearances after 600 or so isn’t going to make a huge difference on a final line, generally; for example, if an average hitter went nuts in the playoffs and posted a 200 wRC+, it might bump his overall wRC+ up by five points or so. For Semien, his seven playoff games would have upped his wRC+ by 15 points to 106. If instead of a 91 wRC+ and 1.2-WAR season (3.2 WAR pace), Semien had a 106 wRC+ and 1.8 WAR (4.8 WAR pace), we might be looking at the context of his free agency in an entirely different manner.

A 30 year old middle infielder coming off 3.8, 7.6, and 4.8 fWAR (or 4.7, 8.9, 0.3 by bWAR) seasons is an immensely desirable player, especially without the risk of losing a draft pick. More to the point, he’s not a player who could be had at just $15-18 million annually over a 3-4 year stretch. But with the peculiar nature of 2020 MLB, Semien didn’t get the chance to prove his offensive outburst in 2019 was a new leaf, after several years of being a roughly average hitter. Semien’s offensive spike is a bit of a mystery, as his uptick in contact seemed to begin in 2018 but didn’t yield a power surge until 2019. 2019 was a doozy for evaluators, as the juiced ball threw many offensive appraisals for a loop, but Semien has had many of the traits of an excellent hitter for years. Moreover, his improvements weren’t centered around BABIP fluctuation, and in fact his 2020 dip was his first major deviation in BABIP, in a supremely negative way. No, his growth came from bolstered power and plate discipline numbers, and at his best his numbers conjure a similar profile to that of Seattle’s most stalwart lineup piece: Kyle Seager.

Baseball Savant’s plate discipline stats attempt to track both the common peripherals - things like how often a player swings at pitches out of the zone vs. within - and more detailed notes, such as their Swing/Take tracker on the specific zones where players have generated more or less value compared to their peers. In fewer words, it attempts to show where a player is getting their plate discipline numbers. Some hitters for instance, run elevated walk rates thanks to being pitched around heavily, but struggle on pitches at the fringes of the zone. Semien, year after year, has put up among the best numbers in the league in the “Chase” zone, just off the plate, where pitchers attempt to lure bad swings. Semien has run double digit walk rates the last two years, and has always had decent free pass numbers, but his excellent acumen in avoiding pitches his opponents want him to swing at has helped him excel. In 2019, Semien notably put together the other part of the equation, finally beginning to do damage on offerings in the “Heart” of the plate, but he gave some of that back in 2020, at least before the playoffs.

Baseball Savant

Still, Semien’s approach has been that of a savvy hitter, and if his projections ring true, the third question above seems encouraging. Semien is one of the faster players in the league, ranking in the 80th percentile by sprint speed in 2020, right in line with the past few seasons. He’s long held Oakland’s leadoff role, and with his high-OBP profile, good speed, and solid power, he’s got the tools to be a potent addition to Seattle’s lineup for several years, at a rate far discounted to what free agents of his caliber often command.

The issue is where to play him. Semien has over 6,700 innings at shortstop in the bigs, with just 401.0 frames at 3B and 236.2 at 2B, but the Mariners aren’t likely to move the reigning Gold Glove winning J.P. Crawford off the position, particularly given the question about his offensive upside. No, for Semien, a signing likely means a relocation to second base, where he could continue to thrive as he has in recent years, flanked by Matt Chapman. With Crawford as his double play partner and Evan White hoovering up anything thrown in his vicinity, Semien’s mixed defensive reputation should shine with the slightly easier defensive task. I wouldn’t have felt comfortable suggesting it until recently, as I do like to hew close to reality in some fashion when proposing fits, but it seems many teams see Semien as a 2B or 3B already in approaching him this winter. According to Robert Murray of FanSided, Semien works out at both spots all throughout the season already in addition to his big league dalliances, so it would hardly be a seismic shift for him. If Semien is an above-average hitter while offering solid defense at second base, he becomes another core component of Seattle’s roster, and offers far more flexibility and depth with Kyle Seager’s looming departure.

I find Semien an unlikely target for Seattle, but considering how many contending clubs have a fit already at shortstop, as well as the numerous massive names looming in next year’s free agency, it’s worth it for the M’s to put their hat in the ring. Teammates and coaches rave about Semien as a leader, and for a club with big dreams and scarcely a playoff appearance or 30 year old beyond the likely-departing Seager to be found, a highly productive veteran with great odds of continuing to deliver is a mighty enticing investment. I would be excited to see Semien in a Mariners uniform after years of being a thorn in Seattle’s side, but I also think he’s the highest the Mariners would reach in this winter’s market. I doubt they go even this high, but the market may surprise us.