Mariners should circle back on unheralded free agent amid trade buzz

After the Seattle Mariners took care of their biggest priority this offseason by signing Josh Naylor to a five-year contract, they have been quiet with adding hitters to their lineup. They lost out on their number two priority in Jorge Polanco, who signed with the New York Mets. Now that they lost him, they might need to turn in a different direction so that they don't get held hostage in a trade.

There are lots of reporters (including Ken Rosenthal of The Athletic) who have linked the Mariners to the notable second basemen on the trade market in Ketel Marte and Brendan Donovan. Both of those players would certainly be upgrades for the M's, but it sounds like the trade cost to acquire those players would be extremely high. Marte has been an elite player for many years, but comes with clubhouse question marks. Donovan has been good not great for a subpar Cardinals team the last few years.

After losing Polanco to the Mets, the Mariners no longer have the leverage to tell teams that they can just go sign him instead of trading prospects for Donovan or Marte. Cardinals fans seem to think they have a superstar on their hands instead of the solid, above average contributor Donovan really is. He would certainly help the Mariners, but he is not worth breaking up the starting rotation for. Instead of being held over the barrel by the Cardinals, the Mariners should pivot to give them leverage.

Mariners should circle back on unheralded free agent amid trade buzz

Not all free agent signings have to be splashy. Sometimes the best deals are the small ones for players when they are coming off of a down stretch, but who had previously been solid. A player who fits that description perfectly is Willi Castro. He was having one of his best seasons in the first half with the Minnesota Twins before being traded to the Chicago Cubs at the deadline. Unfortunately he did not play well at all for the Cubs and hit under .200.

It certainly wouldn't be the sexiest pickup of all time, but Castro would improve the Mariners bench and give them a veteran who can help all around the diamond. The Mariners also lost Dylan Moore last season after he was cut due to his struggles to hit, so the Mariners could use a new utility player. Castro was even a rumored target of the Mariners before the deadline this year.

In 2025, Castro played all three outfield positions as well as second and third base. Those were the positions Dylan Moore played and Castro would help fill a similar role for the Mariners in 2026. In his career he has a .244/.313/.384 slash line with a 94 OPS+, but in his two best full seasons with the Twins in 2023 and 2024, he hit .251/.334/.395 with a 103 OPS+ and was worth 4.2 rWAR.

Those are solid numbers and would warrant getting partial playing time on a playoff contending team. He wouldn't need to be counted on to start every day at one position, but similar to Moore, Castro could move around and help play in certain matchups. Something that would help Castro comparing him to Moore, Castro is a switch hitter so he doesn't have to sit against righties and he has similar numbers against both righties and lefties.

Signing Castro would not cost the Mariners a lot in free agency, likely not more than a couple million dollars. He would fit the roster perfectly because he can take time away from both Cole Young and Ben Williamson in the infield so that they are not overexposed early in their careers and he can also play both corner outfield spots, saving Victor Robles and Dom Canzone from having to play every day. If one or two of those four inconsistent guys play well then Castro could play more at another position and come off the bench. He would improve the flexibility of the lineup and depth chart.

Overall, signing Willi Castro would signal to teams that the Mariners could still trade for another infielder and push Castro further down the depth chart, but the Mariners would not be as desperate to acquire someone for a hefty price on the trade market. The Mariners could tell the Cardinals that they can take or leave their offer because they have an option in house already. Adding Castro and Donovan or Marte sure would be great, but at least having Castro would give the Mariners more confidence navigating the rest of the offseason.