MLB Mock Trade: Seattle Mariners Deal Luis Castillo to Atlanta Braves

Check out this MLB Mock Trade that would send All-Star starting pitcher Luis Castillo from the Seattle Mariners to the Atlanta Braves.

Oct 16, 2025; Seattle, Washington, USA; Seattle Mariners pitcher Luis Castillo (58) throws in the second inning against the Toronto Blue Jays during game four of the ALCS round for the 2025 MLB playoffs at T-Mobile Park. Mandatory Credit: Kevin Ng-Imagn Images | Kevin Ng-Imagn Images

The Seattle Mariners have had a busy offseason as they try to improve their roster and break through to the World Series for the first time in franchise history. Seattle has been active in free agency and on the trade market. One of their final roster questions is who will serve as the backup catcher behind Cal Raleigh. The Mariners could make one more move before the start of the season to address this need, potentially through a trade with the Atlanta Braves.

The Atlanta Braves are dealing with some serious injuries to their starting rotation this offseason. After an impressive 2025 campaign, Spencer Schwellenbach has been shut down because of bone spurs. Breakout candidate Hurston Waldrep was also shut down during Spring Training with elbow inflammation. Both pitchers underwent surgery in February, leaving two open spots in Atlanta’s rotation. Let’s break down a mock trade centered on Luis Castillo that could help fill those holes for the Braves.

Atlanta Braves - Seattle Mariners Mock Trade

Atlanta Braves receive SP Luis Castillo 

Seattle Mariners receive C Sean Murphy, SP Owen Murphy 

In this mock trade, the Braves acquire All-Star starter Luis Castillo. In exchange, the Mariners receive former All-Star catcher Sean Murphy and a young pitching prospect in Owen Murphy.

Fantasy Baseball Outlook

Luis Castillo would slot into the Atlanta Braves’ starting rotation behind Chris Sale and Spencer Strider. He has been very effective for the Mariners since they acquired him from the Reds at the trade deadline four seasons ago. In 2025, Castillo went 11–8 in 32 games with a 3.54 ERA, 1.18 WHIP, and 162 strikeouts. His fantasy value would likely dip if he left Seattle’s pitcher-friendly ballpark. Still, he has proven himself as a reliable, effective starter through consistent performance, and he would play a key role for Atlanta.

With the Mariners, Sean Murphy would serve as the backup catcher behind Cal Raleigh. He would likely see a drop in playing time in Seattle, but this move could also give the Mariners more opportunities to use Raleigh at DH. With the fifth spot open in the Seattle rotation, Emerson Hancock and Cooper Criswell would be viable, experienced options. Alternatively, Kade Anderson and Ryan Sloan are elite prospects who have had strong Spring Trainings and could break camp on Opening Day. The young pitching prospect Owen Murphy would also join a talented farm system and provide a future option for the rotation.