Ken Rosenthal offers insight on several pitchers Red Sox are interested in acquiring
The MLB insider linked Boston to both the Mariners’ Luis Castillo and free agent Jack Flaherty.
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The Red Sox remain in search of starting pitching despite their recent blockbuster trade for Garrett Crochet.
Chief baseball officer Craig Breslow said after the trade that Boston “will continue to be aggressive in our pursuit of any path to improving the team”, whether that means adding a starter and/or right-handed hitter.
The Athletic’s Ken Rosenthal listed multiple arms he says the Red Sox are in on. The insider reaffirmed that the club has “inquired about” trading for the Seattle Mariners’ Luis Castillo, and said they “can not be ruled out for” free agent Jack Flaherty.
Boston has long been linked to several of the Mariners’ starters in potential trade scenarios, dating back to Sept. 13 when Rosenthal floated the idea that the Red Sox could trade first baseman Triston Casas to Seattle in exchange for pitching. The idea turned into legitimate reporting by Rosenthal among others this winter.
Last weekend, The Boston Globe’s Alex Speier reported that a Casas trade isn’t simply a random thought. Speier said Boston is “open” to dealing Casas for arms, but didn’t explicitly mention the Mariners in his story.
“An executive for one American League club said the Sox offered Casas as a headliner in talks about one of that team’s arms, withholding Wilyer Abreu and the elite prospect group (Roman Anthony, Kristian Campbell, Marcelo Mayer) from the proposal,” Speier said.
Whether Casas remains in Boston or not in 2025, it’s evident that the organization isn’t giving up on refining its rotation. Castillo appears to remain a real trade option for them as someone who’s an established, durable arm. The 32-year-old righty owns a career 3.56 ERA, posting a 3.64 in 2024 with 175 strikeouts across 175 ⅓ innings.
Castillo has started less than 25 games just twice in his career: his rookie season in 2017 and the COVID-shortened 2020 season. He’s owned an ERA higher than 4.00 just once (2018), and opponents have possessed a batting average above .250 one time in his MLB career (.255 in 2021).
If the Red Sox indeed want to bolster their rotation, adding Castillo would do just that.
As for Flaherty, Rosenthal also noted that the Red Sox were interested in signing him when he was a free agent last winter. Flaherty ended up inking a one-year deal with the Detroit Tigers. He was traded to the Los Angeles Dodgers at this past season’s trade deadline.
The 29-year-old righty hasn’t performed to the level he did in 2019 when he finished fourth in National League Cy Young Award voting. That said, Flaherty had one of the better seasons of his career in 2024. He owned a 3.17 ERA across 28 starts and struck out nearly 200 batters (194). Flaherty also possessed a 10.8 strikeouts per nine innings and kept his home runs allowed per nine at 1.3.
With top-tier free agent starters such as Blake Snell and Max Fried off the board, Flaherty’s stock is likely to rise as the rest of the league searches for arms. Boston is reportedly hesitant to sign Corbin Burnes, so an arm like Flaherty could make more sense for the club if they don’t want to dish out larger contracts.
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