The Mariners' rotation is unforgivably doing the opposite of what it should be

Last year was a truly special campaign for the Seattle Mariners rotation. It led the majors in a whole host of categories, including ERA, WHIP, opposing team batting average, and fewest walks. This season, however, things have not gone quite as well, with them ranking 15th in ERA, 10th in WHIP, tied-15th in opposing team batting average and 10th in fewest walks.

In fairness to the Mariners, this situation hasn't been helped by injuries to three-fifths of what is considered their preferred starting rotation, in Logan Gilbert, George Kirby, and Bryce Miller. One season after only 13 total missed starts by a fab five which also includes Bryan Woo and Luis Castillo, they've already tallied 33 missed starts.

Now the Mariners finally have their planned starting five back together following Miller's return this past week from elbow inflammation. However, to say things haven't been going well for the rotation of late would be considered an understatement.

Dog days of summer for the Mariners

For the month of August, the Mariners rotation is ranked 17th in the majors with a 4.60 ERA in 19 outings. And on the road, only Colorado Rockies starters have given up a worse wOBA. That the team has managed to go 11-8 despite a vastly underperforming rotation is actually impressive, but when it comes down to it, only Woo is pitching exceptionally well — as he has done for the majority of the season.

The recent nine-game road trip really exposed the rotation's warts, as they played a major role in the M's going just 2-7. Gilbert and Kirby should now be fully recovered from their respective injuries and rolling, but both had their worst outings of the season in their most recent starts.

Gilbert was embarrassed in a 12-7 loss to the Philadelphia Phillies, as he gave up nine hits and six earned runs in just 2.0 innings. Meanwhile it was even worse for Kirby in last Sunday's MLB Little League Classic, as he allowed 12 hits, three walks and seven earned runs in 4.2 innings of a 7-3 loss to the New York Mets.

We'll give Miller some slack for the four hits, two walks and four earned runs he allowed in 5.0 innings against the Phillies in a 6-4 loss, given it was his first game back off the IL. Although keep in the back of your mind that he's been in a funk all season, as evidenced by his 5.87 ERA and 1.509 WHIP being worst among all starters, even including Logan Evans and Emerson Hancock.

Finally we come to Castillo, who has arguably given the Mariners more than was expected this season and has proven to be their second-most reliably starters. However, his 6.05 ERA in August represents his worst month of the season, and he allowed 11 hits, two walks and three earned runs in his most recent outing. He was removed after just 4.0 innings in a 11-2 loss to those blasted Phillies.

A distinct disparity between home and away productivity

One thing that links the quartet is that all four of their poor outings came on the road, which is important to note in respect of how they've performed at home compared to on their travels. The table below gives an idea of the disparity for the Mariners' preferred starting five:

Of course there's a whole myriad of statistics you could look at to further break down the Mariners fab five, but the bottom line is to not give up runs. It's clear Castillo, Gilbert and Kirby are all doing just fine at T-Mobile Park, but struggling tremendously on the road. Woo is the only one pitching well on his travels, while Miller has been poor no matter where he's pitched.

The recent 2-7 road trip was a particularly brutal example, but the Mariners have struggled in general as evidenced by a 31-35 record on their travels in 2025. Clearly not helping this is the rotation's struggles away from Seattle, which plays into the long-known reality that T-Mobile Park is the ultimate pitcher-friendly ballpark.

Overall, some dropoff was expected by the rotation after being the best in baseball last season, but it's been more of a dip than many envisioned. Injuries can no longer be used as an excuse and now it's up to the Mariners' preferred starting five to live up to their collective talent level including producing better on the road, which they are certainly capable of.

In 2024 plenty of people complained about the offense and contended that even an average lineup would have been enough to compliment the M's superior pitching. Well, that offense is now performing above average for the most part this year, but it won't count for much if the rotation doesn't rediscover its mojo to help this team avoid another wasted opportunity to make the playoffs.