SEATTLE – Seattle Mariners Executive Vice President & General Manager of Baseball Operations Justin Hollander announced today the Mariners have acquired right-handed pitcher Seranthony Domínguez, minor league catcher Boston Smith, minor league outfielder Nolan Jones and cash considerations from the Chicago White Sox in exchange for right-handed pitcher Luis Castillo.
“’The Rock’ has been an integral part of this era of our organization’s history,” Mariners President of Baseball Operations Jerry Dipoto said. “His arrival, and subsequent performance in 2022 set the tone for what has been a fantastic run as a Mariner. We all appreciate everything he has done in Seattle and wish him continued success in all he does.”
Domínguez, 31, has appeared in 42 games for the Chicago White Sox this season, going 4-3 with 12 saves, a 4.10 ERA (17 ER, 37.1 IP), 23 walks and 45 strikeouts. Domínguez's 10.85 strikeouts-per-9-innings ranks 15th among American League relievers with at least 30.0 innings pitched this season. Domínguez is signed through the 2027 season.
The 6-foot-1 righty has appeared in parts of 8 Major League seasons with the Phillies (2018-24), Orioles (2024-25), Blue Jays (2025) and White Sox (2026), going 19-17 with 52 saves, a 3.57 ERA (136 ER, 343.1 IP), 158 walks and 405 strikeouts. The Esperanza, Dominican Republic native was originally signed by the Philadelphia Phillies on October 6, 2011.
Smith, 23, has appeared in 78 games across 3 minor league levels in 2026, batting a combined .291 (77x265) with 67 runs, 7 doubles, 3 triples, 22 home runs, 58 RBI, 9 stolen bases, 74 walks, a .448 OBP and slugging .589 for an 1.037 OPS with Class-A Kannapolis, High-A Winston-Salem and Double-A Birmingham. Smith is ranked as the No. 15 prospect in the White Sox system by MLB Pipeline.
The left-handed hitting catcher was selected by the Washington Nationals in the 6th round of the 2025 MLB First-Year Player Draft out of Wright State University (OH). He was traded from the Nationals to the White Sox in exchange for INF Curtis Mead on March 28, 2026. Smith, who was born in Dayton, Ohio, made his professional debut in 2026 in the White Sox organization. He stands 5-feet, 10-inches tall.
Jones, 28, is batting .257 (82x319) with 52 runs, 16 doubles, 1 triple, 14 home runs, 59 RBI, 11 stolen bases, a .362 OBP and slugging .445 (.807 OPS) in 90 Triple-A games between the White Sox and Guardians organizations in 2026.
Jones has appeared in parts of 4 Major League seasons with the Guardians (2022, 2025) and Rockies (2023-24) organizations, batting .247 (263x1,064) with 132 runs, 54 doubles, 7 triples, 30 home runs, 137 RBI, and 33 stolen bases with a .731 OPS. He finished 4th in NL Rookie of the Year voting in 2023 after recording a 20 homer, 20 stolen base season with a .291 average, and a .931 OPS with the Rockies.
Jones was originally selected by the Cleveland Guardians in the 2nd round of the 2016 MLB First-Year Player Draft out of Holy Ghost Prep High School (PA). He has spent time in the Guardians, Rockies and White Sox organizations.
Castillo, 33, is 3-9 with a 5.06 ERA (56 ER, 99.2 IP), 32 walks and 86 strikeouts in 20 appearances (17 starts) with the Mariners this season.
Castillo was originally acquired by the Mariners on July 30, 2022 from the Cincinnati Reds. He signed a 5-year contract extension with a vesting option for 2028 with the Mariners on September 26, 2022. Over 5 seasons in Seattle, Castillo went 43-40 with a 3.69 ERA (294 ER, 718.0 IP), 198 walks, 719 strikeouts and a 1.18 WHIP in 126 games (123 starts). He appeared in 2 postseason runs (2022 and 2025), earning the win in Game 1 of the 2022 American League Wild Card Series and the win in Game 5 of the 2025 American League Division Series.
Castillo has appeared in parts of 10 Major League seasons with the Reds (2017-22) and Mariners (2022-26) with an 87-93 record, a 3.65 ERA (613 ER, 1,510.1 IP), 485 walks and 1,579 strikeouts in 263 appearances (260 starts).