The Mariners’ Latest Pitching Success Story

For years, the Mariners’ largely homegrown rotation has been one of the envies of teams around the league. Logan Gilbert, George Kirby and Bryan Woo have all made an All-Star team in the past couple years. All three have a career ERA of 3.61 or better with better-than-average strikeout and walk rates alike. Bryce Miller hasn’t had as much success relative to his teammates, but he posted a 3.52 ERA with quality strikeout and walk rates in his first 56 MLB starts before an injury-ruined 2025 season (90 1/3 innings, 5.68 ERA, two IL stints for elbow inflammation).

Veteran righty Luis Castillo wasn’t signed and developed by the Mariners, but Seattle pried him from Cincinnati in a 2022 trade for a package headlined by infield prospects Noelvi Marte and Edwin Arroyo. The M’s quickly extended Castillo on a five-year, $108MM deal. In parts of five seasons with Seattle, his 3.61 ERA is right in line with the previously mentioned group (and a near-identical match to his 3.62 mark in six seasons with the Reds).

No organization in baseball has had more continuity in its major league rotation than the Mariners since this wave of pitchers arrived on the scene at T-Mobile Park. They’ve been consistent, productive and, with the exception of Miller’s recent injury issues, largely durable. That’s been key for the Mariners, because one less-talked-about aspect of their strong rotation is that the depth behind the group hasn’t been great.

From 2022-25, the quintet of Gilbert, Kirby, Woo, Miller and Castillo started 75% of the Mariners’ games. (Castillo wasn’t even acquired until July 29 of the 2022 season.) The Mariners had rotation cameos from Robbie Ray (signed to a five-year deal, missed the second season due to Tommy John surgery, then traded to the Giants), Chris Flexen (26 starts on the back end of his low-cost contract) and Marco Gonzales (a holdover from the prior rotation group who was eventually traded while injured). But for the most part, it’s been the same group of five, which has helped to mask the fact that the bulk of their top prospects in recent years have all been position players.

One hopeful addition to the group, for years, was right-hander Emerson Hancock. The No. 6 overall pick in 2020, Hancock was never touted as a future ace. He was an advanced college arm with above-average stuff and good command, one whom Baseball America tabbed as a potential No. 3 starter — “and perhaps better if he refines his breaking pitches.”

Instead, Hancock’s development went the other direction. His command worsened. He lost some life on his fastball as he battled shoulder troubles and a lat strain. In general, he became more hittable. Hancock’s strikeout rate plummeted when he reached Triple-A in 2024, though he still posted a mid-3.00s ERA. He was north of 5.00 in 2025.

Between some infrequent and inconsistent big league stints from 2023-25, Hancock totaled 162 2/3 innings with a 4.81 ERA, one of the lowest strikeout rates in baseball (15.6%) among pitchers with that many innings and a good-not-great walk rate (7.8%). He looked like a fifth or sixth starter — the type of arm who oscillates in and out of a rotation before possibly settling into a bullpen role or beginning to bounce around the league as a swingman.

There weren’t many tangible signs of a breakout last year. Hancock’s average fastball climbed to a career-high 94.9 mph, although that was at least moderately skewed by a move to the ‘pen later in the season. He sat 94.6 mph as a starter in 2025 — still up from his previous career-best 93.4 mph — and 97.2 mph as a reliever. But even with the velo increase, Hancock’s swinging-strike rate fell. His opponents’ contact rate climbed. His 8.1% walk rate was a career-worst mark. Hancock had the look of a depth starter and was entering his final option year in 2026. The long-term outlook wasn’t great.

And then spring training rolled around.