​The Chicago White Sox made a significant addition to their rotation at the MLB trade deadline Saturday, acquiring starting pitcher Luis Castillo from the Seattle Mariners, according to ESPN’s Jeff Passan.Reportedly going back to Seattle are reliever Seranthony Domínguez, outfielder Nolan Jones and catching prospect Boston Smith.The deal is more than a rental. Castillo has significant money on his contract, with a $24.2 million salary in both 2026 and 2027, plus a $25 million vesting option in 2028 that will be determined by how often he sees the mound. The White Sox will absorb all of those obligations, per ESPN’s Alden González.That cost will be balanced out by offloading the contract of Domínguez, who is due $10 million next year.Starting pitching was a clear need for Chicago entering the deadline. They are in first place in the AL Central at 58-52 and have been one of the most surprising teams in baseball, but they also entered Saturday ranked last in MLB in innings pitched by their rotation and 16th in ERA. Castillo isn’t a perfect fix, but there are few of those at the deadline. He has been an above-average pitcher for much of his 10 years in the big leagues, but he has posted career-worst numbers this season at 33 years old and has seen time in the bullpen. He hasn’t seen much improvement recently either, with a 5.48 in four starts in July.That made him expendable for the Mariners, who were 2.5 games out of a wild-card spot entering Saturday.