The Athletic has live coverage of the 2026 MLB Trade Deadline.Trade details: Chicago White Sox acquire right-hander Luis Castillo from the Seattle Mariners for right-hander Seranthony Domínguez, catcher/outfielder Boston Smith, and outfielder Nolan JonesI’ve been writing for a little while that the Mariners needed to kick Luis Castillo to the curb with Kade Anderson marching through Double A like an angrier General Sherman, but the $30 million left on Castillo’s contract — while a sunk cost for Seattle — through the end of 2027 was going to be an impediment to any deal. They found a partner in the feel-good hit of the summer, the White Sox, and even got a real prospect in return along with a platoon outfielder who might help the Mariners right away.Catcher/outfielder Boston Smith was the Nationals’ sixth-round pick last year out of Wright State, where he’d hit .330/.498/.770 with 26 homers, but was a 22-year-old senior in the very mediocre Horizon League. The new front office in Washington traded him before he played his first professional game, sending him to Chicago for Curtis Mead, a deal that worked out for both teams, as Smith has taken off in pro ball. He started in Low A, quickly moved to High A and raked, with the major caveat that 23 is quite old for that level. The Sox promoted him to Double A on July 1 and he’s hit .306/.485/.667 in 23 games, with a 27.8 percent strikeout rate so far, at a level that’s at least appropriate for his age and experience.In the least surprising development ever, Smith has run into trouble at Double A with offspeed stuff, likely far better than anything he ever saw in college or saw more than once or twice a week in high A. He’s missed 42 percent of the time he’s swung at anything that wasn’t a fastball at the new level, in a sample small enough to hope he can bring it down with time and more looks, but also a potential reason to argue the White Sox sold high on him.