9:50pm: Both teams have officially announced the trade.

9:02pm: According to ESPN’s Jeff Passan, the White Sox and Mariners have agreed to a trade that will send Luis Castillo to Chicago in exchange for Seranthony Domínguez, Nolan Jones, and prospect Boston Smith. ESPN’s Alden González adds that the White Sox will take on all of the money remaining on Castillo’s contract.

It’s a major swing for a Chicago squad known to be looking for veteran starting pitching help. The club lost a tight game to the Rays on Saturday, but still maintains a slight lead in the AL Central. Breakout arms Davis Martin and Sean Burke currently headline the White Sox staff. Free agent addition Anthony Kay has offered decent results. The club has filled out the rest of the rotation with Erick Fedde behind an opener and struggling rookie Noah Schultz.

The 33-year-old Castillo is battling through his worst year as a big leaguer. He’s posted a 5.06 ERA in 20 appearances. Seattle made an effort to keep him in a crowded rotation, despite the struggles, after Bryce Miller returned from injury. Castillo operated behind an opener for three games, the first time he’s pitched out of the bullpen in his 10-year MLB career. Seattle now clears its rotation glut, while Chicago picks up an experienced starter with six playoff appearances under his belt.

This is Castillo’s second time getting moved at the deadline. He was shipped from Cincinnati to Seattle in 2022 for infielders Noelvi Marte and Edwin Arroyo and right-handers Levi Stoudt and Andrew Moore. The Mariners parted with a big prospect in Marte, but they were rewarded handsomely on their end. Castillo was a sturdy member of the rotation up until this season. He delivered a mid-3.00s ERA and 30+ starts in each of the past three years.

Castillo’s arsenal began to slip last season. He averaged a career-low 95.0 mph on his four-seamer. The righty had a Stuff+ below 100 for the first time in the majors. While his fastball has ticked up to 95.3 mph, Castillo is down to a career-low 97 Stuff+. His 19.4% strikeout rate and 10.9% swinging-strike rate are the worst marks of his MLB tenure.

More to come…