After locking up Josh Naylor with a five-year deal-checking off their top offseason priority-the Seattle Mariners have taken a quieter approach when it comes to adding more bats. But with Jorge Polanco slipping away to the Mets, Seattle’s plans for reinforcing the infield took a hit. Now, the front office finds itself at a bit of a crossroads: either pay a steep price in a trade or pivot toward a more strategic, cost-effective move.
The Mariners have been linked to a pair of high-profile second basemen on the trade market: Ketel Marte and Brendan Donovan. No doubt, both would be upgrades.
Marte brings dynamic talent and years of top-tier production, though there are whispers about his fit in the clubhouse. Donovan, meanwhile, has been a steady contributor for a struggling Cardinals team-solid, if not spectacular.
The catch? The asking price for either is reportedly sky-high.
With Polanco off the table, Seattle loses a bit of its negotiating leverage. They can’t exactly bluff anymore and say, “We’ll just sign our guy instead.”
And that’s where things get tricky. The Cardinals, in particular, seem to be valuing Donovan like a cornerstone piece, not just a versatile, above-average contributor.
And while Donovan would certainly help the Mariners, it’s hard to justify giving up a key arm from one of the league’s best starting rotations just to make it happen.
So what now? The Mariners could shift gears and circle back to a name that’s flown under the radar: Willi Castro.
Castro isn’t the kind of signing that makes headlines, but he’s the type of player who can quietly make a roster better. He was enjoying one of his best seasons with the Twins before being traded to the Cubs at the deadline. Things didn’t go well in Chicago-he hit under .200-but that down stretch doesn’t erase what he showed earlier in the year or in seasons past.
In fact, Castro fits a need the Mariners have been staring at since parting ways with Dylan Moore. Like Moore, Castro is a utility man who can move all over the field.
But unlike Moore, Castro is a switch-hitter and has shown more consistency at the plate in recent years. In 2025 alone, he played every outfield position along with second and third base-exactly the kind of versatility that gives managers flexibility over a 162-game grind.
Over his career, Castro owns a .244/.313/.384 slash line with a 94 OPS+, but his two best seasons with Minnesota in 2023 and 2024 saw him post a .251/.334/.395 line with a 103 OPS+ and 4.2 rWAR. That’s not just serviceable-that’s the kind of production that earns you a regular role on a playoff-caliber team, even if it’s not as an everyday starter.
And here’s why Castro makes so much sense for Seattle: he’s not going to break the bank. A low-cost deal-likely just a few million dollars-would give the Mariners a veteran utility player who can take pressure off younger infielders like Cole Young and Ben Williamson. He can also spell Victor Robles and Dom Canzone in the outfield, allowing the team to ride hot hands and protect against slumps.
Castro’s ability to hold his own from both sides of the plate adds even more value. He doesn’t need to sit against righties, and his splits are balanced enough to be useful in various matchups. That kind of flexibility can be the difference in a tight divisional race, especially when injuries and slumps inevitably pop up.
Bringing in Castro wouldn’t prevent the Mariners from making a bigger move down the road-far from it. But it would give them breathing room.
It would allow them to approach trade discussions from a position of strength, not desperation. If the Cardinals still want to talk about Donovan, Seattle can engage without feeling like they have to overpay.
If a deal doesn’t materialize, they’ve already shored up their depth.
Bottom line: Castro isn’t a splashy name, but he’s a smart fit. He fills a real need, doesn’t cost much, and gives the Mariners the kind of roster flexibility that contenders covet. And in an offseason where the trade market is full of inflated price tags, that kind of move might be exactly what Seattle needs to stay competitive without compromising their long-term plan.