Diego Castillo Has Finally Hit His Stride in Second Year With Mariners
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Right-handed reliever Diego Castillo has been somewhat of a wild card since being acquired from the Rays last July.
After consecutive disastrous appearances in early May, it seemed as if Castillo had lost what had made him one of the best relievers in baseball over the past few seasons. But he has since caught fire, coming at no better time for a team looking to find the success it had out of the bullpen in 2021.
Following his five-hit, three-run outing against the Phillies on May 9, Castillo looked lost on the mound. His ERA had ballooned to 9.28 and he understandably losing the confidence of manager Scott Servais.
It took six days for Servais to call on Castillo again, and he didn't give the struggling righty a soft landing spot. Instead, he threw Castillo right into the fire, leading by a run and needing two outs to secure a series victory over the Mets with runners at second and third.
Castillo stuck to his bread and butter, firing nine sliders to strike out Starling Marte and Pete Alonso and get the job done. The win may have sparked something in the veteran reliever, who has been electric ever since.
In 9.2 inning pitched since his big outing in Queens, Castillo is running an ERA of 1.86 with 14 strikeouts and just three hits allowed. This has been a drastic shift since the beginning of the season, and Castillo looks revitalized and confident with every dominant performance that goes by.
Castillo does not rely on high spin-rate fastballs at the top of the zone like Paul Sewald or Erik Swanson, rather sticking to a hard sinker and a slider that can be devastating when located well.
His Baseball Savant page and advanced numbers inspire confidence, even when traditional numbers look rather ugly. Castillo has generated plenty of whiffs and continues to avoid barrels. He ranks in the 80th percentile in strikeout rate and 73rd percentile in whiff rate—all while staying in the 76th percentile of barrel percentage.
The one glaring issue has been his tendency to hand out free passes (32nd percentile in walk rate), but he has been improving over his recent dominant stretch. Castillo has been pounding the zone with an electric downward tilt sinker, and a slider that is generating whiffs 37.4 percent of the time.
His FIP is also outstanding, coming in at a sparkling 2.57 through 21 innings pitched. This seems to suggest even better things are on the horizon, and that some bad luck has impacted his slow start.
Last summer’s deal to net Castillo from Tampa was an exciting addition, especially in light of Kendall Graveman's stunning departure. But there was, of course, concern as to why a smart organization—and a contender, no less—like the Rays would let him go. Shoulder fatigue, as well as many struggles down the stretch last year and early this season, heightened these concerns.
Even though his traditional pitching numbers are still quite ugly, it is clear Castillo is back on track. His recent performance combined with his brilliant advanced stats point towards a better pitcher than what his overall numbers show.
Castillo has evidently regained the mound presence that made him one of baseball's most underrated relie and, while the Mariners bullpen has been shaky thus far, his sudden success has seemingly righted the ship a little. With help on the way in the form of Ken Giles, Erik Swanson and a Matt Brash return on the horizon, this bullpen has the potential to be one of the very best in the league once again.
