Arizona Diamondbacks pitcher Jose Castillo throws in the bullpen during spring training practice at Salt River Fields at Talking Stick in Phoenix on Feb. 13, 2025. Rob Schumacher/The Republic / USA TODAY NETWORK via Imagn Images

How D-backs Reliever Was a Missed Opportunity

Originally posted on Arizona Diamondbacks on SI
By Alex D'Agostino | Last updated Nov 24, 2025 10:00 AM ET

The Arizona Diamondbacks' journey through the marathon 2025 season was anything but smooth. Over the course of an injury-riddled, underperformance-laden season, Arizona had to turn to many more than the expected number of pitchers.

One such pitcher that came and went through a difficult season's worth of pitching results was left-handed reliever Jose Castillo.

Castillo was an intriguing pre-season signing by Arizona, and seemed to have a skillset the D-backs could use in their bullpen. His results for Arizona were quite poor, but he went on to have success on multiple other clubs in the 2025 season.

The below article will be updated live with each individual player review and breakdown. Check out the link for all current player review articles:

Arizona Diamondbacks 2025 Player Review: Jose Castillo

Alex D'Agostino

Castillo signed with the D-backs in late January ahead of the season. It was a minor league deal with an invite to Spring Training.

Castillo impressed his coaches in camp, and appeared to be headed toward making the Opening Day roster, but ultimately suffered a left adductor strain in a Cactus League game that held him out of action until mid-April.

Not long following, he was called up by Arizona. In his first game with the D-backs' big league club, he gave up a pair of homers to the Philadelphia Phillies, taking the loss and a blown save.

Castillo got four more chances with the D-backs, but gave up six earned runs over his final 3.1 innings. He was designated for assignment on May 12.

From there, Castillo bounced around, but his numbers were significantly better once away from the pitching-cursed Diamondbacks.

Castillo was picked up by the Mets and pitched to a 2.35 ERA in 16 games. He pitched three innings without giving up an earned run for the Seattle Mariners, and had a 2.45 ERA over five games with the Baltimore Orioles. He is now a free agent.

Jose Castillo: 2026 Outlook

Castillo is not a likely return candidate, although he does stand out as a bit of a missed opportunity for Arizona.

The D-backs were starved for quality left-handed relief in 2025 after the injury to A.J. Puk and the underperformance of Joe Mantiply.

If they could have gotten even a semblance of stability from Castillo (who was solid for the remainder of the season), there may have been some positive results to gain.

But such was not the nature of Arizona's beleaguered pitching staff this past season.