Mariners’ Bryan Woo Injury Scare Exposes Risk Behind Luis Castillo Trade

Meet the first test of Seattle’s post-Castillo rotation.

Aug 16, 2026; Houston, Texas, USA; Seattle Mariners starting pitcher Bryan Woo (22) pitches against the Houston Astros in the first inning at Daikin Park. Mandatory Credit: Thomas Shea-Imagn Images | IMAGN IMAGES via Reuters Connect

Bryan Woo looked like he had officially cleared his road woes for six innings against the Astros.  Then his right shoulder gave them something else to worry about. He held the Astros to two runs on three hits, striking out five over 75 pitches in Seattle’s 3-2 win. But his afternoon ended earlier than expected because of shoulder soreness.

Dan Wilson called the decision precautionary. Woo said it was “nothing I’m concerned about.” His final fastball registered 97 mph, so there was no obvious velocity collapse or flashing red light.

The Mariners made the right call. But shoulder soreness is still shoulder soreness. It’s not a routine inconvenience and sending Woo back out for his next turn may not be as simple as it sounds.

The AL standings are bizarre enough to create the temptation for the M’s to send Woo back out with urgency. The Mariners are 59-66, a record that normally has us discussing September auditions and constructing an offseason shopping list. Instead, Seattle sits only 2 1/2 games behind the final AL Wild Card spot and four games behind Houston in the AL West.

Somehow, their season is still alive which makes Woo essential to the plan. It also puts the organization’s decision to trade Luis Castillo under the spotlight. They moved Castillo because they believed its rotation depth could absorb the loss. The organization had five other major-league starters, with Kade Anderson and Ryan Sloan pushing from the minors.

Could Kade Anderson Replace Bryan Woo in the Mariners’ Rotation?

Now we’re witnessing just how quickly depth can vanish. Castillo could’ve been the insurance policy. Instead, the Mariners cashed that policy in at the trade deadline, and Woo’s shoulder soreness is the first reminder of what they surrendered. The trade isn’t suddenly a disaster by any means, but the risk is no longer theoretical. 

If Woo misses one start, Anderson will generate the most attention. The organization has already designated him as the sixth starter if push comes to shove. He’s dominated Double-A hitters and looks capable of reaching the majors sooner than most expected. He hasn’t thrown a pitch in Triple-A, but neither Bryce Miller nor Bryan Woo did. 

The Mariners are going to give Woo every test and every extra day he needs. Skip a start if necessary. Does that mean we’ll see Kade Anderson? Probably not unless Woo hits the IL. Either way, Seattle traded away its safety net. Now it has to protect the starter it cannot afford to lose.