SF Giants can safely rule out trade with Mariners for former prospect that got away

One of the bigger trade regrets the SF Giants have over the last decade or so has to be trading away pitcher Luis Castillo in exchange for Casey McGehee. It seems a reunion with Castillo is unlikely to be in order this offseason.

The Giants sent Castillo and another minor-league arm to the Miami Marlins in exchange for McGehee as the team was looking to replace third baseman Pablo Sandoval who departed in free agency. It turned out to be a short-sighted move as McGehee did not last long with the team and was replaced by Matt Duffy while Castillo went on to do great things.

SF Giants unlikely to reunite with Luis Castillo

The Marlins were ultimately not the benefactor of Castillo's impressive career as he eventually wound up being an All-Star pitcher for both the Cincinnati Reds and Seattle Mariners. The Giants certainly have to feel like they missed out on him and there has always been some thought that they could try to rectify that mistake.

There were some rumors last offseason that connected the Giants to Castillo that did not come to fruition and it seems that the Mariners are likely going to retain Castillo again this offseason.

He still has two years left on his contract and is coming off another solid campaign. In 2025 with Seattle he had a 3.54 ERA in 32 starts and 180 and 2/3 innings pitched.

The Giants could certainly use someone like that in their rotation and with the team reportedly unwilling to spend big on a free agent starter, the trade route has seemed like a realistic alternative to the Giants signing a pitcher to an exorbitant deal.

The Mariners have been mentioned as a team potentially interested in trading for Bryce Eldridge, San Francisco's top prospect. Perhaps the Giants could land a rotation arm or two in exchange for Eldridge since the Mariners have a number of enticing rotation options.

Alas, it seems Castillo is not in the cards. Still, a rotation arm like Bryan Woo would look nice in San Francisco especially since Woo is a Bay Area native so even if they cannot land Castillo there are still other trade chips that Seattle could have to offer.

The Castillo trade was certainly a mistake and is a reminder that players who are something of an afterthought in a trade can blossom into something wholly unexpected.