Mariners: What’s Going on with Reliever Diego Castillo?

A little over a month into the regular season, the Seattle Mariners’ once-dominant bullpen is surprisingly stuck with the 4th-worst ERA in the American League. Reliever Diego Castillo, a big righty with the capability to excel in high-leverage situations, has been a major part of the Mariners’ bullpen issues.

Through 10.2 innings of work this season, Diego Castillo is sitting with a 9.28 ERA and 2.25 WHIP, and has given up at least one earned run in all three of his most recent outings. He’s been unable to finish the inning in his last two appearances, giving up five earned runs without recording an out on Saturday agains the Rays, and giving up three in the seventh inning in last night’s blowout loss to the Phillies.

Castillo, acquired from the Rays at last year’s trade deadline in exchange for reliever JT Chargois and infield prospect Austin Shenton, has found success in his career with a nasty combination of a 95mph sinker and 88mph slider. However, he’s been unable to locate these pitches on the corners or get hitters to chase on them so far this year, which has resulted in a dreadful .375 opposing BA against Castillo.

It may be minor, but Diego Castillo has lost some movement on both his sinker and slider this season: his sinker has lowered from 26 inches of drop in 2021 to 24.5 in 2022, and his slider has lowered from 31 inches of drop to 29.5 in the same time frame. When a pitcher depends on his pitches to break more than they actually end up breaking (even if it’s just a matter of inches), they can end up leaving pitches over the plate much more often than they’d like to.

With two minor league options remaining, it’s possible we’ll see Castillo head down to Tacoma if he performs poorly in his next appearance.