Oct 16, 2025; Seattle, Washington, USA; Seattle Mariners pitcher Luis Castillo (58) walks off the mound after being relieved against the Toronto Blue Jays in the third inning during game four of the ALCS round for the 2025 MLB playoffs at T-Mobile Park. Mandatory Credit: Stephen Brashear-Imagn Images Stephen Brashear-Imagn Images

Mariners' $108 Million Star Emerging As Offseason Trade Candidate

Originally posted on Fastball on SI | By Zach Pressnell | Last updated Nov 20, 2025 10:32 AM ET

The Seattle Mariners were one of the best teams in the league this year, but they fell short of the World Series as the Toronto Blue Jays won the American League Championship Series.

As the Mariners head into the offseason, there are plenty of huge moves they need to make. Earlier this month, they made the first big move of their offseason by signing Josh Naylor to a huge contract that keeps him in Seattle for the foreseeable future. But the Mariners could make more big moves in the coming months, including potential trades before 2026 begins.

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Bleacher Report's Kerry Miller recently listed Mariners pitcher Luis Castillo as the team's top trade candidate this offseason. Castillo is attached to a massive contract, which could make him difficult to move.

Luis Castillo is the top trade candidate for the Mariners

"It's not likely Seattle would move Castillo. We should probably throw a dart at one of the prospects instead, maybe 21-year-old middle infielder Michael Arroyo," Miller wrote. "But now they've re-signed Josh Naylor, in order to do anything else even remotely noteworthy to improve the roster, passing the buck on the up to $73.3 million still owed to La Piedra sure would help with the bottom line. Notably, Castillo had a full no-trade clause for the past three years, but that has now expired, leaving the M's with far more flexibility to shop him than they had last winter."

Castillo's a very talented pitcher, but his underlying metrics are trending in the wrong direction. He's not striking out as many hitters as he did in his prime years. His fastball is slowing down with each passing year, but he's still producing high-level results on the field.

Castillo's contract is going to make him difficult to move this winter. There aren't going to be many teams in the league who are willing to give up much value in exchange for a veteran pitcher attached to a massive deal.

Still, the Mariners would benefit greatly from trading Castillo and freeing up the money on the payroll.

More MLB: Mariners Star Projected To Sign 2-Year, $43 Million Deal With Angels

This article first appeared on Fastball on SI and was syndicated with permission.

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