How the Mariners assembled and developed the most fearsome rotation in baseball: 'It’s unbelievable what those guys can do'

Seattle’s rotation features an array of arms no hitter wants to face — and they might still be getting better

The 200-inning starter is practically extinct. Just five pitchers cleared the threshold in 2023, down from 36 in 2013, 44 in 2003 and 52 in 1993. Even 190 innings has become a rarity. Last season, 18 teams had zero starting pitchers throw 190 innings. Ten teams had one. The Phillies had two: Aaron Nola (193 2/3 IP) and Zack Wheeler (192 IP).

The Seattle Mariners, though, had three: Luis Castillo (197 IP), Logan Gilbert (190 2/3) and George Kirby (190 2/3 IP).

No team’s starting pitchers logged more innings last year than Seattle’s 901 1/3. And they might throw even more in 2024. Dependence on starting pitching has plummeted league-wide, but the Mariners do not appear to have gotten the memo.

Seattle’s current projected rotation is the culmination of several years of savvy drafting, keen development and knowing when — and when not — to make a blockbuster trade. It is also a group of pitchers who thoroughly embody the organizational philosophy of “Dominate the Zone,” which you’ll see plastered on signs all around the spring training complex and printed on T-shirts worn by players and staff.

Originally introduced as “Control the Zone” in 2016, it’s a mantra that evolved in intensity in recent seasons, as the standards and ambitions of the organization have escalated across the board. But it’s not just a catchphrase thrown around for fun; the degree to which the “DTZ” mentality has been instilled in Seattle’s personnel has gone a long way in cementing Seattle as one of the premier pitching development organizations in the league.

Now, as the Mariners look to bounce back from a disappointing finish to 2023 and the sourest vibes an 88-win team could possibly have, the pressure is on this pitching staff to perform up to its sky-high potential. Even after a busy winter of reallocating payroll and remodeling the lineup, any visions of a return to October for Seattle are reliant foremost on two components: 23-year-old supernova center fielder Julio Rodriguez and a starting rotation that could be the best in baseball.

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‘I don't know how more people aren't talking about it’

In center field for the Mariners for 282 games the past two regular seasons, Rodriguez has had quite the view of his team’s collection of hurlers.

“They’re special. I don't know how more people aren't talking about it,” he said during spring training. “It's unbelievable what those guys can do.”

Rodriguez’s excitement was apparent as he rattled off the projected rotation.

“Obviously, we got [Luis] Castillo, and everybody knows what he's gonna do,” he said matter of factly of the right-hander who will take the ball on Opening Day. “And then you have Logan [Gilbert]. But you know, you got guys like [George] Kirby, Bryce Miller and [Bryan] Woo. Those are impressive guys.”

The trade for Castillo at the 2022 deadline still represents the most aggressive transaction executed by the Mariners’ current front office regime, and it has paid off in spades. Seattle’s decision to extend Castillo through at least 2027 shortly after acquiring him only confirmed his status as an organizational pillar around whom the entire pitching staff could be built. By this point, Castillo’s presence atop the Mariners' rotation has almost become routine, as if he’s been around much longer than a season and a half.

But his importance cannot be overstated. And while at 31 years old he is by definition the elder statesman of this staff, there’s reason to believe he might still be getting better. Though he arrived to his new team with All-Star pedigree already, Castillo quickly acclimated to Seattle’s focus on filling up the strike zone and reaped the rewards. In his first full season as a Mariner, he posted a career-best 20.3% K-BB%, threw a career-high 197 innings and received Cy Young votes for the first time, finishing fifth in the AL race.

Castillo stands alone as the external addition among his rotation mates, with the other four having been signed and developed by the Mariners — just like Rodriguez. A year after signing Rodriguez as an amateur out of the Dominican Republic, Seattle struck gold with two of its first three picks in the 2018 draft, landing right-hander Logan Gilbert and catcher Cal Raleigh, who have already become organizational cornerstones as well.

With Gilbert still just 27, it might seem odd to consider him an established veteran, but among the current starters, he has spent the most time in the Mariners’ rotation. After a breakout summer in the Cape Cod League, an inconsistent junior spring at Stetson dropped him out of contention for the first handful of picks in the 2018 draft. Seattle then happily scooped him up with pick No. 14, projecting his deep arsenal and tall but sturdy frame as that of a prototypical mid-rotation workhorse.

And that’s exactly what he has become. Since his debut on May 13, 2021, Gilbert has spent zero days on the injured list and logged 495 2/3 innings, 13th among MLB starters in that span.

While the hefty workload has proven valuable on its own, Gilbert has continued to modify his repertoire in search of more whiffs and fewer long balls surrendered as he enters Year 4. Logging so many big-league innings this early in his career has also afforded him an added layer of comfort and confidence — plus some extra wisdom that he enjoys passing down to the slightly younger wave of starters who have since joined him in Seattle.

“I like it because it's a different facet,” Gilbert said of his evolving role in the rotation as someone younger starters can look up to. “I don't just show up to throw, and it's not all about me, you know? I try to focus on them a little more and pay attention to what they're doing and all that kind of stuff because so many people did that for me. Before, there were a lot more older guys that have been around a long time that were kind of pouring into me, and now I'm kind of transitioning [to that] in a way.”

Read more: AL West preview: What's in store for the Astros, M's, Rangers, Angels and A's in 2024?

‘It’s the sharpest movement you've seen, and it ends up in the strike zone’

A year after drafting Gilbert, the Mariners went back to the well, selecting another projectable right-hander from a mid-major school in Kirby, who made his MLB debut almost exactly a year after Gilbert’s. With an uncanny ability to throw quality strikes — he walked six batters across 14 starts during his junior year at Elon — Kirby fit in brilliantly with the organization-wide focus on dominating the zone. When his velocity ticked up in pro ball from the low-90s range he occupied in college to regularly hitting 97 mph deep into starts, his ceiling jumped from “strike-throwing No. 4 starter” to something much greater.

And while there have been many college control artists whose stuff failed to translate to MLB, Kirby has thus far managed to sustain his elite skill set at the highest level. In his 18th career start, he threw 24 straight strikes to start the game, an MLB record. His 9.05 strikeout-to-walk ratio in 2023 was the fifth-best by a qualified starting pitcher in the past century, just behind 2002 Curt Schilling (9.58 K/BB) and a smidge ahead of 2000 Pedro Martinez (8.88 K/BB).

“The ball explodes out of his hand, the pitches do different things, and it's in the zone,” said Mitch Garver, one of the newest Mariners and a recent member of the rival Rangers. “It's really hard to game-plan against. It’s the sharpest movement you've seen, and it ends up in the strike zone.”

Said Castillo through interpreter Freddy Llanos: “The way he's able to attack the zone no matter what the count is, you know, I think that's very impressive.”

The secret behind Kirby’s mastery of command? A nine-pocket net in an empty gym. Seriously.

"My offseason is a lot different than a lot of people,” he said. “I just throw into nine pockets. Just really, like, target-oriented in the offseason, just focused on hitting those little boxes. It’s a very underutilized piece of equipment.”

Wait, what?

“I don’t really throw to catchers until I come [to spring training],” he clarified, noting a stark departure from the bullpen sessions we’ve grown accustomed to seeing pitchers throw all winter.

“It can be a little boring sometimes, but I think it just locks me in. I'm practicing with targets so that when I get into a game, it's just subconscious. I practiced throwing to this spot thousands of times, so now let's throw it there. I just wanna be as precise as possible.”

It’s hard to argue with the results.

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‘This guy understands how to pitch’

Given his intense commitment to his craft, it might seem like Kirby would’ve dominated the zone in any organization. But what makes Seattle’s organizational philosophy especially compelling is the effect it has had on pitchers such as 24-year-old righty Bryce Miller, who begins his second season with substantial buzz in the organization and around the industry. While Kirby was practically allergic to walks at Elon, Miller’s collegiate career — which began at Blinn Junior College before he transferred to Texas A&M — hardly resembled that of a control artist. He walked 18 batters in 28 2/3 innings at Blinn and 57 in 110 2/3 frames as an Aggie.

“I was all over the place,” he said. “My last year at A&M was my first year starting. It was a roller-coaster year, but yeah, ever since I got here, the mentality has been to just attack and throw my best stuff over the plate. Just being in the zone, getting ahead — it's proven it gives you an incredible advantage.”

“It's a mindset, for sure,” said lefty reliever Gabe Speier, who enjoyed a similarly dramatic turnaround after four up-and-down seasons in Kansas City’s bullpen. “When you hear, ‘Throw it down the middle,’ and you have the best hitters in the world standing in the box, it can be like, ‘Really, is that what you want me to do?’

“I think the biggest thing was they instilled confidence in me. And just showing me that getting ahead really helps. … I really took that to heart.”

While Kirby led all qualified starting pitchers in 2023 with a 69.5% first-pitch strike rate, Speier led all relievers at 78.2%, a massive leap from the 52.6% he ran as a Royal. As a team, the Mariners threw 64.5% of first pitches for strikes in 2023. That’s the second-highest mark by a team since pitch tracking began in 2002.

That Seattle’s staff has been able to pound the strike zone to a historic degree while possessing high-end strikeout stuff is what makes it so exceptional, and it exemplifies the graduation from merely controlling the zone to downright dominating it. It wasn’t long ago that Mariners pitchers’ velo routinely ranked near the bottom of the league: In 2019, their starters’ average fastball velocity ranked 29th in MLB at 91.6 mph. That has changed in a hurry as the current wave of starters arrived: In 2023, the rotation averaged 95.1 mph on their heaters, fourth in baseball.

It’s no coincidence that 95.1 mph was also the average fastball velocity for Miller, who threw his fearsome four-seamer more often than all but four starting pitchers in baseball (min. 1,500 pitches). It’s one thing to have the heater, but it’s another to be willing to throw it in the zone to the best hitters on Earth. Like Speier, Miller just needed a little encouragement from the right people. And once he trusted his stuff, a switch was flipped, and he climbed the MiLB ladder in a flash. Among 127 pitchers with at least 100 IP in 2023, Miller’s 4.8% walk rate was ninth, giving the Mariners three pitchers in the top 10 along with Gilbert (eighth, 4.7%) and Kirby (first, 2.5%).

Granted, it wasn’t a perfect rookie season. Miller faded down the stretch and struggled against lefty bats, something he focused on this winter with the development of a splitter to complement his fastball. But in an offseason rife with speculation that Seattle would trade from its wealth of young starting pitching to upgrade its lineup, it became clear that the team was reluctant to give up not only Miller’s potential but also his magnetic off-field personality. Because beyond his remarkable adherence to the directive to throw a boatload of strikes, Miller makes an impact with the way he fits into the organization as a person.

“Whatever is going to come out of his mouth every morning is always a surprise because he's not afraid to just leave himself out there,” manager Scott Servais said. “... That's just who he is. And I think his teammates appreciate that. And that's why he fits into so many different pockets within our clubhouse. … Anybody in that clubhouse, he can go talk to.”

It’s rare enough for a rookie to arrive in the big leagues comfortable with himself, but for a pitcher to become one of the most popular teammates among both his fellow hurlers and position players? That sets Miller apart.

“It's a very unique personality,” Servais said. “I love it. It's straight Tex, and he has fun with that. He's got the hat, he's got the boots, and so there's a little bit of that cowboy facade.”

But make no mistake: “This guy's into analytics. This guy understands how to pitch, how to shape his pitches. He gets all that stuff, and he's very interested in it. He wants to continue to learn more. He's got a growth mindset. Deep inside, he's really driven to be an awesome pitcher.”

Read more: After breakouts last season, these starters are focused on getting even better in 2024

The Mariners' rotation, almost entirely homegrown, could be the best in baseball this year. (Taylor Wilhelm/Yahoo Sports)
The Mariners' rotation, almost entirely homegrown, could be the best in baseball this year. (Taylor Wilhelm/Yahoo Sports) (Taylor Wilhelm/Yahoo Sports)

‘People underestimate how young they are and how much they're learning’

A month after Miller made his Mariners debut, Bryan Woo followed. Selected two rounds after Miller in the 2021 draft, Woo also charted an unusual path to Seattle’s rotation. The pandemic canceled his sophomore season at Cal Poly, and then Tommy John surgery cut his junior year short before he could increase his draft stock to any meaningful degree. Yet despite a lackluster 6.49 ERA in just 69 1/3 NCAA frames across three tumultuous seasons, Woo’s athleticism and silky-smooth delivery enticed Seattle’s scouts and analysts to offer him a $318,000 signing bonus.

That decision was vindicated in short order, as Woo reached Seattle less than two years after signing. In two years of professional baseball since then, Woo has already thrown three times as many innings as he did in three years of college ball, and he looks like a staple of the Mariners’ rotation for years to come.

That said, like Miller, Woo struggled against opposite-handed opponents as a rookie. It wasn’t just that each of them was getting beaten by lefty bats; it’s also that they were both so dominant against right-handed hitters that they remained viable options.

The splits:

  • LHB vs. Woo (180 PA): .283/.389/.540 (.928 OPS)

  • LHB vs. Miller (255 PA): .303/.358/.558 (.917 OPS)

  • RHB vs. Woo (191 PA): .179/.226/.268 (.495 OPS)

  • RHB vs. Miller (282 PA): .200/.234/.315 (.549 OPS)

While the disparity is an obvious red flag that Woo will need to address sooner rather than later, there’s a high level of confidence that he has the physical and mental aptitude to make the necessary adjustments in short order.

“Both those young guys did an awesome job for us last year,” Servais said of the pair. “They learn a lot their first go-around through the league. They also learn how quickly the league adjusts to them. You gotta continue to get better, and both those guys are in the right spot as far as that goes.”

“I feel like people underestimate how young they are and how much they're learning,” Rodriguez said.

Offered Raleigh: "Just excited for them to take that next step. They’re a lot of fun to catch, and they've got really great talent. I think they're both up for the challenge.”

Zooming through the system together, Miller and Woo actually leapfrogged another arm drafted higher than either of them. Emerson Hancock was the sixth overall pick in the 2020 draft, a reward for Seattle’s dismal, 95-loss 2019 in the depths of the rebuild. Hancock made his way to Seattle last year as well before a shoulder strain ended his season prematurely, and after a solid — and healthy — spring, he was looking like a tremendous luxury as Seattle’s projected No. 6 starter.

But the reality of attrition is one that every pitching staff must confront at some point — sometimes even before Opening Day. The recent news that Woo will start the season on the IL due to elbow inflammation was a sobering reminder that no team can survive a full season with just five starters. Now Hancock will be pressed into action sooner than expected, joining a rotation that still expects to do great things.

“It makes you better,” he said earlier this spring of the stacked depth chart ahead of him. “It makes everybody better because you get to see how good everyone is, and you know that everyone's holding themselves to a high standard. And we all want to win a lot of games.”

Last year, the Mariners’ plans to rely heavily on lefties Robbie Ray and Marco Gonzales were altered by significant injuries in the early going. But thanks to Miller, Woo and Hancock, Seattle was uniquely prepared to withstand those absences. There doesn’t appear to be quite the same depth this year beyond Hancock, but the Mariners have earned the benefit of the doubt when it comes to producing reinforcements on the mound. So while it’s highly unlikely that the current crew will make it through all 162 (and beyond) unscathed, the Mariners seem prepared to navigate whatever obstacles lie ahead.

“Our organization does a great job on the pitching side of things,” Raleigh said. “It makes us really confident that we can come up with guys, and we can have the arms, and we can sustain this for a while.”