Is Korean Slugger Si-Hwan Roh the Right Fit for the Mariners at Third Base?

The Mariners have a reason to look at Si-Hwan Roh beyond the power. They would have to figure out whether he can actually hold down the position where they need him. The concept gets buried quickly when a hitter hits the market with 29 home runs and a .505 slugging percentage. Seattle needs offense, Roh has supplied plenty in South Korea, and he would be a much needed addition from the right-hand side.

But the case for signing him starts with his glove. The Mariners need to improve on defense. If they believe Roh can handle third base every day, he becomes an intriguing way to add power and address a position of need in the same move. If their evaluation points toward first base or DH, they likely don’t have much room for conversation.

Josh Naylor already occupies first. Seattle needs to get this roster into better working order, and every addition should have a clear role.

Roh’s Third Base Defense Should Drive the Mariners’ Evaluation

The Hanwha Eagles are moving forward with posting Roh for MLB teams. He’s entering his age-26 season after slashing .283/.360/.505 with 29 home runs over 571 plate appearances in 2026.

He followed a career-best 32-homer season in 2025 with another productive year and has been Hanwha’s regular third baseman for four seasons. Roh would bring an established professional track record to Seattle. The question is how much of that package carries over.

World Baseball Network raised concerns about his range and athleticism at third, suggesting first base could become his eventual MLB home. It’s an assessment worth examining, rather than a verdict we should accept. Seattle’s scouts would need to determine if he could handle everyday work at the position. Maybe they could live with ordinary defense if the bat is good enough.

There is also a reason to keep expectations grounded at the plate. Roh struck out in 25.7 percent of his plate appearances in 2026, while his walk rate fell to 8.9 percent. Those numbers deserve attention as he prepares to face MLB pitching. His power gives Seattle something to pursue; the contact questions give the club something to prove through its evaluation.

That is also where Roh’s age makes this interesting. At 26, he’s giving Seattle a chance to add a hitter whose power is already established and whose approach still has room to grow. We should expect an adjustment period, but there is a worthwhile development bet here.

With CJ Gillman joining as hitting coach, the Mariners have an opportunity to show what their renewed emphasis on hitting development can accomplish. Roh would arrive with a clear strength and a specific challenge: keep the damage while making better swing decisions against MLB pitching. Seattle would need an individual plan for which pitches he can attack, where opponents are likely to expose him and how to adjust when they do.

That makes Roh an intriguing fit for the direction the Mariners want to take. The defensive evaluation still has to support the signing. If Seattle believes Roh can handle third base, his age and offensive upside make him worth pursuing. The Mariners could fill a need today while investing in a player who has room to become more valuable.

Then they need to keep adding. Roh deserves the chance to develop without carrying the responsibility for fixing Seattle’s offense. Give him a position, a clear hitting plan and a stronger lineup around him.

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