Bryan Woo: Seattle's new ace?
The Mariners have a new Cy Young contender.
Not long ago, I suggested Bryan Woo may eventually be considered the gem of Seattle’s vaunted rotation. Considering how his season has started, Woo could potentially achieve this lofty distinction much sooner than anyone expected.
Through his first six starts, Woo is top-15 in multiple categories such as ERA, quality starts, walk rate, WHIP, and FIP. However, this sample size is too small for a serious-minded conversation. So, I combined Woo’s numbers from last year with his 2025 stats. From there, I compared the Cal Poly alum to his peers. The results build a compelling case that Woo is on the brink of greatness.
Unless otherwise noted, the following rankings compare 120 starting pitchers, including Woo, who have faced at least 500 hitters since the beginning of the 2024 season. For reference, Woo has faced 619 batters.
Best wOBA in baseball
Weighted On-Base Average (wOBA) is a sabermetric version of on-base percentage (OBP). It credits a hitter for how he reached base rather than treating all on-base events equally, as OBP does. For instance, a single is more valuable to run production than a walk, a double is more valuable than a single, a home run is more valuable than a double, etc.
For the purpose of our discussion, the wOBA of opposing hitters helps shed light on a pitcher’s effectiveness at limiting offensive production. In the case of Woo, he sits atop a leaderboard populated with an impressive array of names, including fellow Mariners Logan Gilbert and Bryce Miller.
wOBA Leaders (2024-2025)
Bryan Woo (.244)
Tarik Skubal (.249)
Paul Skenes (.249)
Logan Gilbert (.251)
Zack Wheeler (.263)
Hunter Greene (.263)
Tyler Glasnow (.265)
Yoshinobu Yamamoto (.265)
Max Fried (.266)
Bryce Miller (.268)
Garrett Crochet (.270)
Sean Manaea (.275)
Michael King (.276)
Chris Sale (.278)
MLB wOBA for starters = .315
Stingy with the walks
It’s common knowledge that George Kirby is the best in baseball at avoiding walks. That said, Woo has been nearly as good as the Elon product.
Lowest Walk Percentage Among Starters (2024-25)
George Kirby (3%)
Bryan Woo (3.2%)
Zach Eflin (3.3%)
Miles Mikolas (4%)
Joe Ryan (4%)
Tarik Skubal (4.4%)
Nick Martinez (4.4%)
Spencer Schwellenbach (4.5%)
Logan Gilbert (4.7%)
Zack Littell (4.8%)
Shota Imanaga (4.8%)
MLB Walk Rate for starters = 8.4%
An extremely low walk rate undoubtedly contributed to Woo’s league-leading wOBA. But there’s more to it than that. After all, his wOBA is 33 points better than Kirby’s even though their walk rates are almost identical. So, what separated these two talented arms?
Batted ball success
Don’t get me wrong, the currently injured Kirby is an outstanding pitcher. However, the opposition has been more productive against him than Woo on batted balls. Woo has the ninth lowest AVG (.205) and fifth best SLG (.324) since the beginning of 2024, which is much better than Kirby (.245 AVG/.394 SLG).
Barrel avoidance
Woo’s low SLG can be traced back to his ability to minimize the most damaging type of contact - barrels. Statcast defines a “barrel” as a batted ball event with the ideal blend of launch angle and exit velocity. Since Opening Day 2024, these extremely well-struck balls have produced 86-percent of all home runs, a .710 AVG, and a 2.374 SLG.
All told, only seven starters boast a better barrel rate than Woo.
Lowest Barrel Rate (2024-25)
Andre Pallante (4%)
Hunter Brown (4.7%)
Ranger Suárez (4.9%)
Justin Steele (5%)
Cristopher Sánchez (5.2%)
Paul Skenes (5.2%)
Max Fried (5.2%)
Bryan Woo (5.3%)
Spencer Schwellenbach (5.3%)
Luis Severino (5.6%)
Reese Olson (5.6%)
MLB Barrel Rate for starters = 8.2%
xwOBA!
Expected Weighted On-Base Average (xwOBA) is a Statcast product that takes the elements of wOBA and then uses quality of contact (exit velocity and launch angle) to determine what should’ve happened to batted balls. It is my metric of choice for assessing pitcher performance.
A key advantage to xwOBA is defense, good or bad, is removed from the equation. Therefore, we get a truer sense of how a pitcher is doing without the influence of his teammates’ defensive acumen.
Only Paul Skenes of the Pirates has a better xwOBA than Woo. Impressive considering Skenes started last year’s All-Star game for the NL and subsequently earned Rookie of the Year honors. It’s also worth noting that Woo is slightly ahead of reigning Cy Young Award winners Tarik Skubal (AL) and Chris Sale (NL).
Top xwOBA (2024-25)
Paul Skenes (.252)
Bryan Woo (.259)
Zack Wheeler (.261)
Tarik Skubal (.261)
Chris Sale (.268)
Tyler Glasnow (.269)
Hunter Greene (.269)
Justin Steele (.271)
Joe Ryan (.271)
Garrett Crochet (.271)
Logan Gilbert (.272)
MLB xwOBA for starters = .319
For this nerd, Woo’s superior xwOBA is the hallmark of a pitcher blossoming into one of baseball’s best.
Rotation review
So far, we’ve compared Woo to a large group of big-league starters. But our titular question was Mariners-centric. So, let’s consider how he stacks up against the main contributors to Seattle’s rotation: Gilbert, Miller, Kirby, and Luis Castillo.
Woo leads the starting staff in multiple categories, although several rotation-mates are slightly better than him in a few areas. Still, the sixth-round draft pick being elite at avoiding quality contact (xwOBA and barrel rate) and preventing walks stands out to me in a big way.
Have arm, will travel
As Mike Petriello chronicled earlier this year, T-Mobile Park is easily the most pitcher-friendly venue in MLB. Yet, Woo was superb whether he was pitching in the Emerald City or on the road.
Granted, Woo was better at home. But this is to be expected considering the depressing effect T-Mobile Park has on offense. Having said that, his numbers on the road are excellent. Other than strikeouts, the Oakland, California native is significantly better than the average MLB starter even when away from the ballpark at the corner of Edgar & Dave.
Yeah, but…
Everything covered thus far has established the foundation for a good news story. But we need to consider an issue concerning some Mariners fans - Woo’s health.
In the last eight years as a collegian and professional, Woo has logged 492 innings with 62-percent of this workload occurring since the beginning of the 2023 campaign. To me, this is an intense ramp-up considering his injury history since the COVID-19 pandemic.
Having said that, the Mariners have a great reputation for developing and protecting arms. So, I’ll defer to the organization on what’s best for their pitchers. Furthermore, previous injuries aren’t necessarily predictive of future health challenges.
Then again, it’s understandable if a segment of the fan base wonders whether Woo having arm-related issues in three of the past four seasons is an ominous indicator of what awaits the right-hander and the Mariners.
Well?
Is Woo Seattle’s ace? With Kirby and Gilbert sidelined with injuries, the current answer is a resounding yes. But will Woo still be the titleholder at season’s end?
Tough to say at the moment. But it’s important to remember that the 25-year-old Woo is relatively inexperienced and already trending towards Cy Young Award contender status. Knowing this, I wouldn’t bet against him emerging as the best of the bunch.
My Oh My…