Scouting Report: Diego Castillo

Summary

Luis Castillo (note: sources reference Luis Castillo, not Diego Castillo) is experiencing a difficult 2026 season with the Seattle Mariners. After posting a 6.29 ERA and 1.66 WHIP over 34.1 innings in his first seven starts, the Mariners are considering removing him from the rotation when Bryce Miller returns from injury. Castillo has allowed at least four runs in six of his last seven starts and has been moved to a piggyback/bulk reliever role. His spot in the starting rotation is tenuous, with the team exploring options including a six-man rotation, bullpen role, or potential demotion. Despite his struggles, the team is proceeding cautiously given his track record as a three-time All-Star and his inability to pitch in relief at the major-league level previously.