The Seattle Mariners had well documented offensive issues for much of the 2024 season, but one thing they could almost always count on was solid defense at an important position: third base.

That’s probably not going to be the case in 2025, at least at the start of the season.

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This offseason, Seattle did not tender a contract to Josh Rojas, who was the team’s primary third baseman in 2024. He was statistically one of the best players defensively at the position, but he isn’t much of an offensive threat. So instead, the Mariners are going into 2025 with Jorge Polanco penciled in at the hot corner.

Polanco has much more power and a higher ceiling at the plate than Rojas, but he’s not known for his defense. And in fact, he’s not really that familiar with third base. The 31-year-old switch-hitter came up as a shortstop with the Minnesota Twins and has primarily played second base since 2021. In his MLB career, he’s appeared at third in just 24 of his 917 games.

The Mariners recently brought Polanco back on a one-year contract for 2025, and it’s a move MLB Network insider Jon Morosi termed as “not a bad risk.” But Morosi isn’t sold on Polanco as a third baseman, especially since the Mariners are built around their elite starting pitching and put a high priority on suppressing runs.

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“I’m just not sure how that looks in the end because he’s been a middle infielder for basically his entire career,” Morosi said Wednesday during his weekly conversation with Seattle Sports’ Wyman and Bob. “So now he’s going over to third base, he can probably handle it, but this is a pitching and defense team that needs third base to be played at an above-average level, I believe.

“Yes, (Seattle’s pitchers) miss plenty of bats, but that’s a really crucial defensive position to have someone at a relatively advanced baseball age – at least a mid-career player – move there and do it for the first time in the major leagues. So yeah, I heard (Polanco will be the Mariners’ third baseman) and raised an eyebrow a bit at at that.”

The Mariners may have a backup plan if Polanco’s defense isn’t up to par, though, and it’s one that’s pretty intriguing defensively even though it has gone under the radar at this point.

Keep your eye on Ben Williamson

The Mariners’ farm system is loaded with players ranked in the top 100 of all baseball prospects by various publications, but that doesn’t mean there aren’t other prospects in the organization who could help the big league club.

Specifically in this case, there’s 24-year-old third baseman Ben Williamson, a second-round 2023 MLB Draft pick by Seattle out of the College of William & Mary.

Williamson spent the majority of 2024 with Double-A Arkansas, and his numbers at the plate were solid but not eye-popping (.273/.365/.374 slash, .749 OPS, three home runs in 95 Double-A games). It’s his glove that makes him interesting, though, and it’s easy to see a scenario this year where the Mariners want to keep Polanco’s bat in the lineup as the designated hitter while Williamson comes up to provide a defensive upgrade at third.

The MLB Pipeline profile of Williamson calls him “a plus defender at the hot corner who will prevent runs for whatever pitching staff he plays behind, and he can even move to shortstop when needed. His success is rooted in his body being in sync, having the instincts to read tough hops to go along with above-average arm strength.”

Mariners assistant general manager Andy McKay raved about Williamson to Seattle Sports’ Brock and Salk just this week when he spotlighted some prospects to watch this spring.

“Recently he graded out in one of the industry sources … as arguably the best defensive infielder in Minor League Baseball. And whether he is or isn’t, he’s definitely in that conversation,” McKay said. “High baseball IQ, tremendous competitor. He was a part of that championship team in Arkansas last year and is just a true professional.”

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Mariners general manager Justin Hollander also pointed at Williamson, who is one of the team’s non-roster invitees to MLB spring training, as an option at third when he joined Seattle Sports’ Bump and Stacy in studio Wednesday.

“(He’s) an awesome defender who advanced through Double-A last year, will likely start a Triple-A this year,” Hollander said, “and you’ll see a lot of Ben at third in spring.”

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