Mariners Rumors: Starting pitching trade buzz coming into focus

With the Winter Meetings now officially over, Seattle fans may be disappointed in the lack of concrete moves made by the team. However, while a significant portion of the front office returned to Seattle last week, Jerry Dipoto stayed in Texas, allegedly to hear more from parties interested in trading for Luis Castillo.

The most interested organization seems to be the Boston Red Sox, who have turned their attention to the team's ace after initially setting their sights on acquiring one of the team's younger starters.

Shortly after acquiring Kyle Tucker, the Cubs were reportedly still making a concerted effort to pick up Castillo as well. Daniel Kramer, who provides coverage of the Mariners for MLB, also listed the Phillies, Orioles, and Yankees as other teams seeking starters and in possession of infield talent that would interest Seattle in a potential trade.

What has heated up Castillo's market so quickly? For teams looking to bolster their rotations, he might be one of the best remaining options. With Max Fried, Blake Snell, Nathan Eovaldi, and a whole slew of other starting pitchers now committed to brand new free agent contracts, there aren't many arms left on the board. Corbin Burnes, Jack Flaherty and Sean Manaea are arguably the only enticing pitchers remaining, and all three could bring on undesired financial constraints, especially Burnes who could be aiming for a contract in the realm of Fried's $218 million deal.

Castillo wouldn't be cheap either, with $72 million over three years and a vesting option in 2028 still remaining on his contract, but he's remarkably consistent for his pay grade.

In his eight-year major-league career, he's only had an ERA above 4.00 in one full season (2018). Since becoming a Mariner, he has accumulated a 3.43 ERA over 437 2/3 innings with 9.7 K/9. He's good at limiting walks, expanding the zone, and has one of the best four-seam fastballs in the sport.

His secondary pitches have become less effective over time and the changeup with which he built his legacy in Cincinnati is thrown less frequently with each passing year. He's also lost a bit of velocity on his heaters, going from an average velocity of 97 mph in 2022 to 95.6 mph in 2024. These may be cause for concern, but he would still make for a dependable ace or strong No. 2 guy in almost any team's rotation.

With the front office's dogged determination to maintain their young core of starting pitchers, Castillo could now become the team's most valuable trade asset. He'll only be let go for the right haul, but it's encouraging to hear that Seattle is ready to make necessary moves to meaningfully improve their roster for 2025.