Mariners Season Primer: Pitching

The Mariners will go as far as the pitching staff takes them in 2024, which could end up being the Fall Classic.

Ross D. Franklin / AP Images

We’ve previously previewed the Mariners’ offense. So, let’s turn our attention to the pitching staff. But before discussing the upcoming season, we should first reflect on what Seattle pitchers accomplished in 2023.

A year to remember

The lineup may have struggled to hold up its end of the bargain last season. But pitching was the club’s core competency - its strength - much like it was in 2022. Evidence of this superiority becomes obvious when we review the stats - Seattle pitchers were top-3 in multiple categories.

In the case of the rotation, it thrived despite losing 2021 AL Cy Young Award winner Robbie Ray, Marco Gonzales, and Easton McGee to season-ending injuries.

Pacing the staff was Seattle’s Big Three: Luis Castillo, Logan Gilbert, and George Kirby. Behind them were Bryce Miller, Bryan Woo, and Emerson Hancock. Three youngsters filling the void created by injuries. Granted, Hancock suffered a shoulder injury after his third start. But his presence covered Woo’s short IL stint.

Naturally, if we’re talking pitching I’m going to mention my go-to stat - xwOBA. Seattle’s starting staff produced a sixth-best .311 xwOBA among MLB rotations. All told, four starters had an xwOBA better than the league-average: Woo (.289), Gilbert (.297), Castillo (.302), and Kirby (.307). The lone Mariner missing the mark was Miller (.337).

Expected Weighted On-Base Average (xwOBA) uses quality of contact (exit velocity and launch angle) to determine what should’ve happened to batted balls. A key advantage to xwOBA is defense (good or bad) doesn’t influence it. This gives us a truer sense of how a hitter or pitcher is performing. Last year, the MLB average xwOBA for starters = .326

It’s worth noting Woo’s .289 xwOBA tied with reigning AL Cy Young Award winner Gerrit Cole and Boston’s Kutter Crawford for 12th-lowest among 148 starters facing 300-plus hitters. To me, this is a clue as to why the Mariners were reluctant to trade the right-hander in the offseason.

Delivering distance and quality were distinguishing characteristics of the rotation in 2023. Castillo, Kirby, and Gilbert each logged at least 190 innings - only 12 other pitchers across MLB accomplished this feat.

Pitchers with 190+ innings in 2023
SEA - Luis Castillo/Logan Gilbert/George Kirby
PHI - Aaron Nola/Zack Wheeler
SFG - Logan Webb
HOU - Framber Valdez
STL - Miles Mikolas
MIN - Pablo López
PIT - Mitch Keller
BAL - Kyle Gibson
ARI - Zac Gallen
NYY - Gerrit Cole
MIL Corbin Burnes
TOR - Chris Bassitt

In the quality department, look no further than the 74 quality starts made by Seattle last season - only the Twins (76) and Padres (75) had more. Naturally, Kirby (20), Castillo (18), and Gilbert (18) were top-15 in this category.

Having said all that, we can’t overlook the late-season swoon experienced by the rotation. During our November conversation bemoaning the foolishness of trading a starter, I noted opponents produced the highest OPS of the year versus Seattle starters in September and October. This suggests to me the staff was running on fumes.

Compounding matters for manager Scott Servais, this decrease in overall effectiveness resulted in a noticeable drop in starter usage in September and October. This led to the bullpen covering at least 10 extra innings during a pivotal point in Seattle’s postseason chase.

Speaking of the relief corps, it boasted the lowest xwOBA (.293) among big-league bullpens. Eight Mariners facing 75-plus hitters bested the MLB-average for relievers (.312).

Paul Sewald - .216
Andrés Muñoz - .268
Justin Topa - .268
Trevor Gott - .275
Trent Thornton - .278
Matt Brash - .280
Gabe Speier - .290
Isaiah Campbell - .306

It's worth noting Tayler Saucedo (.314) just missed the cut. That said, the Tahoma High School product was a valuable contributor to last year’s bullpen.

As you already know, some names listed above are no longer Mariners. Paul Sewald was traded in an unpopular deadline deal; Trevor Gott was shipped to the Mets along with Chris Flexen earlier in the season; both Justin Topa and Isaiah Campbell were included in player swaps over the winter.

Now that we’ve covered last year, let’s discuss two great concerns I have about the rotation - health and depth.

Breaking news

Just today, the Mariners reported Woo will begin the season on the IL with elbow inflammation. GM Justin Hollander informed the media, including Ryan Divish of the Seattle Times, Woo’s injury is similar to the one sidelining him last August. Hancock will once again step in for the Californian.

Woo’s injury history and previous workloads have always cast a shadow of doubt over his durability. The Cal Poly product underwent Tommy John surgery and had never thrown over 70 innings in a year as a collegian or professional until 2023 when he logged 131.2 frames with Seattle and Class-AA Arkansas.

Bryan Woo’s Collegiate/Professional Inning Totals

2018 - Summer Lg (24.1)
2019 - NCAA/Summer Lg (49)
2020 - NCAA (17.2)
2021 - NCAA (28)
2022 - MiLB/AFL (67.2)
2023 - MiLB/MLB (131.2)

My main takeaway from the preceding list is 70-percent of the innings Woo has thrown as an adult happened last season. He’s 24-years-old, folks.

To be clear, I’m not second-guessing the wisdom of the Mariners counting on Woo to be part of the upcoming season’s starting rotation. Far from it. But the injury risk associated with the sophomore seems much higher than it did yesterday.

So many injuries

Here’s a nugget bound to send some already-anxious Mariners fans into a further tizzy. Castillo, Kirby, and Gilbert all throwing 190-plus innings was a great accomplishment and a great fun fact to share. However, it’s worth mentioning that six of the 14 pitchers reaching 190 frames in 2022 didn’t make 25 starts the following season due to injury or suboptimal performance.

To be fair, there’s no way to predict future injuries with accuracy. Furthermore, each member of the Big Three has remained relatively healthy during his respective career. Castillo did miss 35 days in 2022 with shoulder soreness. But that’s his only arm-related issue. Kirby dealt with shoulder fatigue in 2021 as minor-leaguer and has been fine ever since.

Still, consider how many prominent starting pitchers are currently battling health-related issues that have cropped up during Spring Training.

A Sample of Injured Starters Across MLB

Gerrit Cole - Elbow discomfort
Justin Verlander - Shoulder soreness
Kodai Senga - Strained shoulder
Kevin Gausman - Shoulder soreness
Eduardo Rodriguez - Strained lat
Sonny Gray - Strained hamstring
Eury Perez - Elbow inflammation
Kyle Bradish - Sprained elbow
Lucas Giolito - Elbow surgery
Bryan Woo - Elbow inflammation

Next man up, then what?

Even if Woo returns quickly from the IL, the rotational depth behind Hancock is precariously thin. Remember, 13 pitchers started games for the Mariners last year. Six are no longer with the club. One holdover from 2023 was a reliever, who served as an opener.

Seattle’s 13 starters

Luis Castillo - 33 starts
Logan Gilbert - 32 starts
George Kirby - 31 starts
Bryce Miller - 25 starts
Bryan Woo - 18 starts (IL/workload constrained)
Marco Gonzales - 10 starts (injured)
Chris Flexen - 4 starts (pulled from rotation)
Emerson Hancock - 3 starts (injured)
Tommy Milone - 2 spot starts
Robbie Ray - 1 start (injured)
Easton McGee - 1 start (injured)
Trent Thornton - 1 start (opener)
Luke Weaver - 1 start (opener)

Unlike last year, there isn’t a bevy of no-brainer options like Miller, Woo, Hancock, and Taylor Dollard waiting in the wings. All that remains from that group is Hancock, who’s just been thrust into action again. It’s also worth noting the sixth overall pick of the 2020 draft has pitched over 100 innings in a season just once in his life. Last year, when he suffered a season-ending shoulder injury.

Levi Stoudt and Jhonathan Díaz may be possibilities. There are certainly others I’m not aware of. After all, management has a better grip on its pitching inventory than this nerd. Perhaps time will prove I was overreacting to the rotational depth situation. But I don’t believe I am.

Better keep Tacoma on speed dial

Per Spotrac, the Mariners had just three relievers on the IL last year: Gott, Andrés Muñoz, and Penn Murfee. The team has already matched this tally and we haven’t even reached Opening Day.

Matt Brash is dealing with elbow inflammation, while the big offseason addition to the bullpen, Gregory Santos, is resting a strained lat muscle. Another winter pickup and early-favorite to earn a bullpen spot, Jackson Kowar, will miss the year following Tommy John surgery.

To me, it would be wishful thinking to believe Seattle’s bullpen will remain as healthy as it did in 2023. Three is easily the lowest number of injured relievers the team has accrued in a full season since the current front office took over in September 2015.

Number of M’s Relievers on the IL

2016 - 8
2017 - 7
2018 - 7
2019 - 9
2021 - 11
2022 - 8
2023 - 3

MLB average number of injured relievers in 2023 = 7

Fortunately, Brash and Santos are expected to rejoin the bullpen during the upcoming season, which is promising. But as we know, the recovery time and prognosis for pitcher injuries can vary greatly by individual. Therefore, I suggest taking a wait-and-see approach with both relievers until they’re back and performing up to expectations.

To mitigate the risk of potentially losing Brash or Santos long-term, the Mariners recently signed former Astro Ryne Stanek. The seven-year veteran made 55 relief appearances for Houston in 2023. Stanek’s .311 xwOBA, 23.9-percent strikeout and 9.5-percent walk rates were league-average for a relief pitcher. But the 32-year-old did experience a nearly four-point decline in his strikeout rate from the season prior (27.7-percent).

That said, Stanek continued to throw very hard. Only 17 relievers registered more pitches with a velocity of 98 mph-or-greater than the 335 delivered by the former Arkansas Razorback. Just ahead of Stanek on the list: Santos (355) and Muñoz (346).

Stanek has remained relatively healthy during his seven big-league seasons - an important consideration at the moment. According to Sportac, the right-hander has been on the IL three times in the last five seasons. His injuries weren’t arm-related.

Stanek injuries

2019 - Hip soreness (23 days)
2020 - COVID-19 (31 days)
2023 - Ankle sprain (17 days)

Another notable bullpen addition was Austin Voth, who we discussed about a month ago. The University of Washington alum has experience as a starter and a reliever.

Perhaps Voth will be eventually considered a depth option for the rotation. The six-year veteran’s career stats suggest better success as a starter. Since we’ve been focusing on health, it’s important to note the 31-year-old missed 71 days last year due to elbow discomfort.

Here’s my best guess at who begins the season in Seattle’s bullpen.

Projected Opening Day Bullpen

Andrés Muñoz
Ryne Stanek
Collin Snider
Cody Bolton
Trent Thornton
Austin Voth
Tayler Saucedo
Gabe Speier

Regardless of which eight relievers make the club, one thing is certain. There will be considerable bullpen churn throughout the season - even if Brash and Santos both return and remain healthy and effective.

Last year, the Mariners used 25 relievers (including position player Mike Ford). That was in a season when the team saw just three relief pitchers on the IL. In no particular order, here’s a long list of potential candidates to help.

Seattle’s Current Reliever Pool

Tyson Miller
Mauricio Llovera
Ty Adcock
Carlos Vargas
Eduard Bazardo
Brett de Geus
Joey Krehbiel
Ty Buttrey
Jhonathan Díaz
Kirby Snead
Sean Poppen
Heath Hembree
Peyton Alford
Travis Kuhn
Marcelo Perez
Cory Abbott
Blas Castano
Casey Lawrence
Matt Brash – injured
Gregory Santos – injured

Please note several of the names listed above may no longer be Mariners by Opening Day. We’re currently in that period when clubs trim rosters to a more practical size.

Postseason bound?

Yes, health is always a consideration. It’s the great equalizer for any organization, even for the really good ones. But fretting about future injuries, as if they’re a certainty, isn’t the way to enjoy baseball.

To me, the Mariners’ starting rotation is the class of the AL West and perhaps MLB - even with Woo heading to the IL. Think about how great it is for Seattle to have a young, dynamic arm like a Bryan Woo slated to be its number-five starter and have the ability to slot in an Emerson Hancock when Woo unexpectedly goes down. Some clubs were still scrambling over the weekend to round out their rotation.

Despite the injuries to Brash and Santos, it’s tough to bet against the Mariners organization when it comes to finding talented relief arms and then helping them thrive. And let’s give Servais, pitching coach Pete Woodworth, and the rest of the pitching brain trust credit for maximizing the performance of the bullpen.

What I see in the Mariners’ pitching staff is the foundation for a World Series contender. Obviously, the trick is reaching the dance to make noise in October. The team fell short of this objective in an utterly disappointing fashion last year. I suspect the current stable of arms won’t allow a repeat of this failure in 2024.    

My Oh My…