Mariners' initial win in Luis Castillo trade is rapidly turning into a nightmare loss

Let's go back to the 2022 trade deadline. Hot in pursuit of their first playoff berth in decades, the Seattle Mariners acquired Luis Castillo from the Cincinnati Reds. He had been a key piece of Cincinnati's rotation since being called up in 2017, and was poised to lead what was at the time an underwhelming starting pitching unit in Seattle.

Because of his established reputation and the Mariners' need, he didn't come cheap. Seattle conceded four prospects, three of which were in the organization's top 10. Nonetheless, Castillo fulfilled his role and helped lead his new team to the playoffs. They were so satisfied with his numbers that they offered him a five-year, $108 million contract extension in September of that year, preventing him from becoming a free agent.

This is the third season of that deal and unfortunately, it seems like Castillo is headed in the wrong direction.

Luis Castillo is fading just as Noelvi Marte is rising

He's no longer saddled with the burden of having to be the franchise ace given the amount of young talent that now fills the roster, but he has gotten progressively less dominant with each passing season.

Things have come to a head after the All-Star break, as Castillo has posted a 5.17 ERA over his nine second-half starts. He has given plenty of hard contact to opposing hitters and his four-seam fastball is the only pitch that has accumulated positive run value.

When viewed as a whole, his numbers as a Mariner are far from bad. Yet it's important to remember that with a salary north of $24 million, he's the highest paid member of the team. With two more years and a potential sixth year that vests based on time spent on the injured list, the Mariners could still end up paying $70 million for a declining starter.

Meanwhile, the most valuable component of the return package, Noelvi Marte, has been having a breakout season.

He didn't get off on the best foot with an 80-game PED suspension and -1.8 rWAR in 2024. But this season, he has become a valuable piece of the Reds' lineup. He has posted a 124 OPS+ over his 277 plate appearances and looks like he'll be holding down right field in Cincinnati for the foreseeable future.

Castillo isn't the only arm that's suffering from second half struggles. Logan Gilbert hasn't been the same since being shelved with an elbow injury and George Kirby has been uncharacteristically shaky over the past few weeks. But Castillo is the only pitcher that has already demanded a high prospect and financial cost from the Mariners while arguably failing to reach peaks as high as his homegrown peers.

The Mariners are on the edge of a total collapse and are dropping the ball on their playoff push. Other than Julio Rodríguez and Bryan Woo, everyone else on the roster has run into a brick wall and is having a hard time being as effective as they were earlier in the season.

Luis Castillo's regression is at best a temporary issue and at worst a financial sandbag that limits Seattle's ability to play competitive baseball. He doesn't need to lead the rotation, but if the Mariners want to remain legitimate contenders through September, he'll at least have to be more of an asset than a liability.