Mariners Make a Decision on Luis Castillo-Bryce Miller Tandem
Having six healthy starting pitchers is usually a luxury in Major League Baseball. For the Seattle Mariners, however, it has created an unusual pitching situation.
Rather than returning to a six-man rotation, Seattle is expected to continue using a piggyback approach with starting pitchers Luis Castillo and Bryce Miller, according to The Seattle Times' Adam Jude.
The tandem is expected to take the mound again Sunday in Seattle's series finale against the Arizona Diamondbacks.
Jerry Dipoto acknowledged the piggyback is "still not an ideal solution," but the club believes it's the best option for now, and he's confident all parties are on the same page now ... https://t.co/SPFGcTiRcD
— Adam Jude (@A_Jude) May 27, 2026
Seattle first adopted the piggyback strategy on May 19 against the Chicago White Sox. Miller, 27, pitched brilliantly in just his second start of the season after returning from a left oblique strain. He allowed just one hit and one walk over 5.2 innings while striking out seven hitters.
Castillo then followed Miller out of the bullpen for his first career regular-season relief appearance.
The plan nearly worked perfectly. Castillo held Chicago scoreless into the ninth inning before surrendering a walk and a hit-by-pitch to the first two White Sox hitters. After striking out the next batter, he was pulled for Andrés Muñoz, who allowed both inherited runners to score in Seattle's frustrating 2-1 loss.
Despite the defeat, the plan nearly ran flawlessly and Seattle used the strategy again Monday against the Athletics. This time, Castillo started while Miller worked out of the bullpen in Seattle's 9-2 victory.
Castillo allowed two hits and two walks while striking out six across four scoreless innings before being replaced by Miller. However, the veteran right-hander was visibly frustrated after being removed from the game.
Another look at Luis Castillo after learning that his night was done.
— Daniel Kramer (@DKramer_) May 26, 2026
Can't recall ever seeing this kind of frustration in his nearly four years with the Mariners.
"We knew that was part of the plan, and you've got to respect what his decision was." pic.twitter.com/goDRAmc262
"As a competitor, you kind of want to go out there and continue," Castillo said. "But at the same time, you've got to respect his position. We knew that was part of the plan, and you've got to respect what his decision was."
Monday also marked Miller's first career relief appearance, a transition the 27-year-old admitted was both unfamiliar and uncomfortable.
"I just didn't really know how I was going to navigate it," Miller said. "I think I've got [76] starts over the last four years, plus a couple of years in the Minor Leagues. Like, I haven't done this in a while -- really, since college -- pitching out of the bullpen. So, I didn't really know how to navigate it. But I just did the best I could."
Following his return from injury, Miller appeared headed for a temporary bullpen role given his workload challenges and three IL stints since the start of last season. Yet, Miller has looked great since his return, and Seattle does not want to disrupt his momentum. Miller owns a 1-0 record with a 2.25 ERA across 16 innings over three appearances (two starts) this season.
Castillo, meanwhile, has been Seattle's most inconsistent starter in 2026. The 33-year-old right-hander is 1-5 with a 5.90 ERA across 11 games (10 starts) and 50.1 innings.
The piggyback approach also emerged because of Emerson Hancock's breakout. Initially expected to serve as a temporary fill-in arm, Hancock has arguably been Seattle's best starter this season. He owns a 4-2 record with a 2.78 ERA across 11 starts.
The remainder of Seattle's rotation includes George Kirby, Logan Gilbert, and Bryan Woo.
At the moment, it remains unclear whether the Mariners will eventually return to a six-man rotation. But for now, Seattle appears committed to continuing its Castillo-Miller tandem.
The Mariners will look to complete a sweep of the Athletics today at 3:05 ET and move into first in the AL West.
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This story was originally published May 27, 2026 at 7:21 AM.