Mariners right-hander Luis Castillo left Sunday’s game due to a strain in his left hamstring, and will undergo an MRI on Monday to assess the damage. Castillo told reporters (including Adam Jude of the Seattle Times) via interpreter that some discomfort first arose in the fourth inning when he moved on the mound to evade a throw that never came from catcher Mitch Garver on an Ivan Herrera stolen base. Two pitches after Herrera’s steal, Castillo grimaced on the mound after his follow-through, and left the game after a visit from trainers.
“The discomfort’s there. Tomorrow we’re going to get some [tests] done, just to see what it is, but hopefully it’s not too bad,” Castillo said.
With the Mariners battling for either the AL West title or a wild card, losing Castillo would put a serious dent in the club’s playoff hopes. Seattle ranks at or near the bottom of the league in several major offensive categories, yet the M’s have been carried by their elite rotation. The rotation has been both effective and durable — of the 21 starters who have tossed at least 161 1/3 MLB innings this season, four of them (Castillo, Logan Gilbert, George Kirby, and Bryce Miller) pitch for Seattle.
Bryan Woo has had a pair of IL stints, with Emerson Hancock stepping into the rotation in Woo’s place to take nine starts. Hancock (currently at Triple-A) is the likeliest candidate to return to the staff if Castillo has to go on the injured list, yet the former top prospect hasn’t been very consistent against big league hitters. Hancock has a 4.76 ERA in 45 1/3 innings and a 4.50 ERA in 12 innings in his 2023 debut season, and only a 13.8% strikeout rate in his brief MLB career.
While Hancock is a better sixth starter than most clubs possess, there’s still no easy way to replace Castillo. The three-time All-Star hasn’t been quite as effective as he was when finishing fifth in AL Cy Young Award voting in 2023, but Castillo still has a 3.64 ERA over 175 1/3 innings this year. His strikeout and walk rates are still above the league average, and while Castillo’s four-seamer has dropped in velocity from 96.3mph in 2023 to 95.5mph this season, it remains one of the most effective pitches in baseball.