Mariners could come face-to-face with an impossible playoff conundrum

Things have been looking great for the Seattle Mariners. Currently riding a six-game win streak, their momentum is at a season peak and, while they must be wary not to get ahead of themselves, a postseason berth now seems like a foregone conclusion.

However, making it to October and being a legitimate contender are two different things. The bracket will start with a total of 12 teams, but only one will have the honor of hoisting the World Series trophy. Attempting to make a deep run brings about its own set of questions to be answered.

The first will come up in September when MLB rosters officially expand from 26 to 28 players. Seattle has plenty of talent to choose from to fill those last two spots, and could leverage some of the existing depth that's slated to return from injury soon.

The second will arise when it comes time to decide to set the starting rotation for the playoffs.

Who should be the Mariners' Game 1 starter in the playoffs?

With relatively long breaks in between series and a constant threat of elimination, picking the right arm to toe the slab for any given postseason contest could be the difference between a first-round exit and a pennant victory. Seattle is blessed with one of the best rotations in MLB, even if their season ERA of 3.91 doesn't necessarily reflect that. One downside of having such a well-rounded group of arms is that there isn't a clear choice to lead the pack.

Logan Gilbert has been perceived as the team's ace for the past two years, but since he returned from the injured list in mid-June, he hasn't looked nearly as dominant. Prior to hitting the shelf, he had a 2.37 ERA for the season and is now at a 3.35 ERA after his last 10 starts. Of those outings, only two were considered quality starts. The biggest inhibitor has been a lack of efficiency. Despite pitch counts between 85-95, he has only made it through six innings twice in the past two months.

Bryan Woo is on the opposite end of the spectrum and has served as a bastion of consistency on the mound. He already has thrown over 140 innings to a 3.02 ERA and is set to have the best season of his career by a comfortable margin. However, we're now in uncharted territory, as we don't know whether his increased workload will lead to regression in the final portion of the season. Furthermore, it's a lot to ask to have someone with no playoff experience to lead your rotation.

George Kirby's season has been filled with ups and downs after taking the ball for the first time in 2025 in late May. After a very rocky first month, he has been back to his usual self, posting a 3.12 ERA from June 1st onward. Although he seems to be trending in the right direction, one interesting wrinkle in his game continues to affect him adversely. He has a walk rate of 6.3 percent, almost twice as high as his career average. Coupled with declining peripherals on his slider and sinker, he's not a clear step above the other members of the rotation.

Logan Evans and Bryce Miller would be fighting over the same roster spot and neither player has a compelling case to be the ace. Miller has been making progress on the road to recovery, but is far from ready to pitch six strong innings against other contending teams. A true rookie, Evans has been a good back-of-the-rotation option but isn't nearly experienced or dominant enough to be an October ace.

Last but not least is Luis Castillo. He had some tough outings in April and June but he was outstanding in July, posting a 2.05 ERA over five starts and has carried that success into August. Unfortunately, he has been susceptible to hard contact all year, posting barrel and hard-hit rates in the bottom quartile.

While a home run here or there in the regular season can quickly be brushed off, separate articles by FanGraphs and MLB suggest that teams that hit more home runs tend to win playoff games. That could exacerbate what has been Castillo's main weakness this year.

Compared to teams that are still fighting tooth and nail to get into the postseason, this is the definition of a first-world problem. However, it's one that's all the more important to a franchise that is still the only one in MLB to never win a pennant. While other teams are trying to cement their existing legacies, the Mariners are still trying to get theirs off the ground.

On the bright side, they seem to have plenty of talent to work with. On the other hand, if it's mismanaged, it could be another frustrating year of watching it all go to waste.