Seattle promotes RHP Luis F. Castillo to start Friday, designates RHP Hagen Danner for assignment

Luis F. Baby and the F is for fastballs.

The Seattle Mariners announced Friday that they have selected the contract of RHP Luis F. Castillo, and have designated RHP Hagen Danner for assignment. Castillo will start today’s game in San Francisco, in a delightful bit of serendipity to follow up veteran starter RHP Luis (M.) Castillo who started Wednesday’s victory over the Detroit Tigers. For the purposes of this article, all future references to “Castillo” will be in regards to Luis F. Castillo, unless otherwise specified. We wrote up Castillo in our 2025 non-roster invitees article during Spring Training, and his writeup has been transposed below for your ease:

It’s not like “Luis Castillo” is an uncommon name, exactly – it’s no Brady Feigl – but to put both Luises F (Felipe) and M (Miguel) Castillos in the same organization feels like a recipe for trouble. Maybe the Mariners thought they’d be able to trade Original Flavor Castillo during the off-season? The new Castillo (F) looks to make a resurgence into pro ball after spending the last two years pitching overseas in Japan; he’ll be easy to visibly distinguish from the other Castillo (M), as he’s significantly more slightly built than the Mariners’ workhorse, and also will be entering from the bullpen rather than starting on the mound. Also, he doesn’t appear to have the beautiful flow our Luis Miguel enjoys; get wrecked, Yankees. Still, we’re not counting out a few Parent Trap-type hijinks this spring. F-boy Castillo whips in a sweeping slider in the low 80s that’s been a chase-inducer in NPB and helped him run an enticing groundball/whiff combo that is ideal for run prevention. He’ll vary the motion to throw a similar breaker with far greater vertical bite and get those delicious grounders, as will his upper-80s changeup that may be his nastiest pitch. The fastball is more pedestrian, in the 91-93 range as a starter in Japan, but the full kit is effective. -KP and JT (bet you can guess which is which)

Castillo’s spring went well enough, earning himself a spot with the Tacoma Rainiers this year after 94.1 IP with the Orix Buffaloes in NPB with a 2.96/2.45 ERA/FIP in 2024. Though he actually was stellar with the Detroit Tigers during his big league debut in 2022, not allowing a run or a walk in 3.2 frames, Castillo took greater job security and the chance to start at the highest level of the sport outside MLB in 2023 with the Chiba Lotte Marines of NPB, before returning for another tour of duty with Orix.

This will be Castillo’s first start as a big leaguer, having been a reliever for most of his professional career before rejuvenating his skillset in Japan. Signed originally with the Arizona Diamondbacks as an international amateur back in 2012, the same year as his teammate of the same name, though two years younger than The Rock. The Pebble (credit to Daniel Kramer of MLB) is his own person, and not a longtime big league ace, but does have some resemblance in his delivery. Long levers whip across Castillo’s body from a sidearm angle, coming over the top of the ball for significant sinking movement that aims to generate grounders. His first start of the year went well in Tacoma, and the goal will be to create more grounders than punchouts.

Shuffled off is Danner, who has a chance to clear waivers and stick in Seattle’s system. Claimed off waivers in January, the righty reliever still has interesting arm talent, but has been a career reliever whose 2023 debut was an espresso sip more than a cup of coffee, retiring the only batter he faced.