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Mariners 2021 Free Agent Target: Sung Bum Na

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A better-late-than-never look at one of South Korea’s best sluggers.

Doosan Bears v NC Dinos - Korean Series Game 3 Photo by Han Myung-Gu/Getty Images

At 2 PM PST today, this article’s relevance will likely expire. That’s when the posting period for Korean Baseball Organization star Sung Bum Na will end, and with a glut of similarly profiled players, the 31 year old slugger may be destined to return to the NC Dinos. The market for clobberin’ corner outfielders is crowded, the track record for KBO sluggers coming to MLB is shaky, and a few quality players from KBO and NPB have already passed on offers to come to the U.S. or been passed on by clubs. Still, Jerry Dipoto has gone to Korea for three players already in his tenure, bringing a pair of ex-pat pitchers home in Chris Flexen and Seth Frankoff along with a similar Korean veteran slugger in Dae Ho Lee, though Lee had five years as a NPB stalwart after a decade of KBO stardom prior to joining the M’s. Na may well see a star role in Korea as preferable to part-time work in the States, but if his desire to give MLB his all still burns strongly enough, he could be the lefty bat the Seattle Mariners remain focused on.

Sung Bum Na has been a balanced threat in the KBO for much of his career, with 20+ home runs in six of his eight seasons as a pro, and all seasons in which he received at least 500 PA. He’s been a double-digit base-stealing threat as well, with solid efficiency for much of his career, though the brutal knee injury he sustained on an awkward slide in early 2019 has had some impacts on his athleticism, albeit not on his offensive success. He ran a .324/.390/.596 line in 2020 with 584 PA, 34 home runs, and a 155 wRC+, with a >.300 batting line every year since 2014 and an ISO >.200 all but once since then. Scouts seem to view Sung Bum Na as a below-average defender at this point, though not unplayable in the outfield especially thanks to a strong arm. Seattle could create a sort of grim symmetry in their outfield, joining Kyle Lewis and Mitch Haniger for a trio of players immediately able to commiserate on grievous injuries that needn’t waylay future success. If Seattle remains, as Jerry Dipoto recently said, “open to the idea if the right bat, part left-handed bat, fell to us,” there’s an upside opportunity here so long as the club appears unwilling to flex their massive unspent cash on higher-tier players.

LL aLLum Brendan Gawlowski wrote for FanGraphs on Na when he was posted in December that the market was likely to be meager for the Scott Boras client, and that has borne out. Unlike countryman Ha Seong Kim, positional versatility and youth are not on his side. Kim had the recent example of Jung Ho Kang to point to for on-field success in a similar profile, while Sung Bum Na faces many of the questions on his ability to deliver the same impact at the plate as other KBO transplants due to the velocity gap and overall quality difference in the average pitcher. Though he idolizes Shin Soo Choo, Choo famously came to the U.S. at just 18 years old, growing accustomed to the pitching earlier.

Na’s strength comes from a thick frame which he leverages into a leg kick and massive torque. He handles low pitches best and can go down to get off-speed with some impact even when fooled. Unfortunately, Na’s strikeout numbers were high even in KBO at around 25% this year, a career-high after years around 20-21%. Much like Kyle Lewis, some of Na’s strikeout rate is a byproduct of his tendency to work longer plate appearances, putting himself one whiff away from a K in search of a good pitch to drive. He’s been able to overcome that with his power in Korea, but it’s less clear if he’d have similar success against hotter heat and sharper breaking balls in MLB.

There are plenty of possibilities Seattle could go for, even with Kyle Schwarber garnering $10 million guaranteed ($18 million possible) for a year and an option with the Nationals today. Joc Pederson, Michael Brantley, Eddie Rosario, Jurickson Profar, Nomar Mazara, and others remain out there, most likely for more money and more confidence in success. If Seattle wants a player to make them more likely to contend in 2021, Na is a low-confidence addition. With the club doubtful to make a move that puts them in a likely contention situation, however, Sung Bum Na would be a more interesting flier for the spot Jarred Kelenic will likely soon occupy than most.