Mariners at Memorial Day: Rotation

The roster's strongest unit is arguably the best in baseball. But it shouldn't be taken for granted.

John Froschauer / AP Images

With Memorial Day weekend upon us, enough time has elapsed to have a serious conversation about the Mariners’ 2023 campaign. We’ve already discussed the team’s run production effort. Now, let’s turn our attention to the roster’s strongest unit - the starting rotation.

League leaders

President of Baseball Operations Jerry Dipoto, GM Justin Hollander, and their staff have managed to make starting pitching a core competency of the organization. Even better, the following array of stats suggest the Mariners currently have the best starting five in baseball.

Fans from other markets may not agree with my assessment. But Seattle’s starting staff leads MLB in multiple categories and is top-three in several others, including a metric I’m always drawn to - xwOBA.

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 = .323

Anyone who’s read my work at Prospect Insider and now with this newsletter is familiar with my fondness of xwOBA. To me, it’s an ideal metric for gauging pitcher effectiveness since it reflects key functions central to pitching success: minimizing contact; avoiding base runners; preventing the most damaging batted balls.

Among 153 starters facing at least 100 batters this season, four Mariners have an xwOBA within the top-25: Bryce Miller, George Kirby, Logan Gilbert, and Luis Castillo.

xwOBA of Current M’s Rotation (and AL Ranking)
Bryce Miller - .256 (3rd in AL)
Logan Gilbert - .268 (7th)
George Kirby - .284 (16th)
Luis Castillo - .298 (22nd)
Marco Gonzales - .349 (59th)

MLB average xwOBA = .323

It’s important to acknowledge Miller has just five starts on his big-league résumé. But the Texan has taken the league by storm in those five outings. Miller’s four-seam fastball has the lowest opponent AVG, SLG, wOBA, and xwOBA among starters who’ve thrown 300-plus four-seamers.

Last year’s breakout starter, Kirby, is even better in 2023. Friday’s ugly start notwithstanding, the Elon alum has performed like a staff ace. Provided good health continues, we may be witnessing the beginning of a Cy Young Award candidacy.

Having said that, we shouldn’t exclude Gilbert from early Cy Young conversations. The 14th overall pick of the 2018 draft ranks fifth in the American League in strikeout rate, sixth in walk rate, second in WHIP, and seventh in fWAR.

And let’s not overlook the team’s Opening Day starter, Castillo. The Dominican Republic native got off to a great start before going through a minor slump. He’s since rebounded with his fWAR, ERA, K%, and WHIP ranking no worse than eighth in the junior circuit.

That brings us to the Mariners’ fifth starter - Marco Gonzales. His overall numbers may not look great. But that’s largely attributable to a pair of clunkers against Boston and Toronto. The totality of the former Gonzaga Bulldog’s seven other starts are quite respectable.

Yes, I’ve just performed a cherry-picking exercise with Gonzales’ stats. One placing him in a favorable light. I’m not suggesting he’s a Cy Young candidate or a top-of-the-rotation arm. But the southpaw undoubtedly provides value to Seattle’s starting staff.

Perhaps management takes the rotation in another direction at some point in the future. One which doesn’t include Gonzales in the starting five. But for now, the longest-tenured Mariner deserves to take the ball every five days.

Youth served

Age may be the most exciting element about Seattle’s rotation. Three starters are 26-or-younger. The “graybeard” of the staff is Gonzales, who’s 31.

Ages of M’s Starters
Bryce Miller (24)
George Kirby (25)
Logan Gilbert (26)
Luis Castillo (30)
Marco Gonzales (31)

Still, there’s an important factor to consider with so many youthful arms in the rotation at the same time - workload management.

Miller, who was drafted in 2021, threw 133.2 innings last year. That’s essentially what the Texas A&M product tossed in three college and summer league seasons (137.1). This year, he’s logged 51 frames with Seattle and Class-AA Arkansas.

In 2022, Kirby pitched 156.2 innings with the Mariners, Arkansas, and Class-AAA Tacoma. But consider this; last season was the first time he threw over 100 frames as a collegian or professional.

Prior to his debut in 2021, Gilbert had thrown 100-plus innings during his college and minor-league careers. However, the Stetson product didn’t pitch competitively in 2022 due to the COVID-19 pandemic.

As a rookie, Gilbert threw 124.1 innings with Seattle and Tacoma. Last season, he ramped up to 185.2. This year, the right-hander has 60 frames under his belt, which puts him on a pace to log 192 in 32 starts.

To be clear, I’m not suggesting Miller, Kirby, and Gilbert need pampering - they don’t. But it’s reasonable to expect management will exercise caution with its three young guns. After all, Seattle’s success this season and in future campaigns hinges on the availability and effectiveness of its top starting pitchers.

Farm aid

If the need arises this season, there are potential minor-league options to help shore-up the rotation. The Mariners have already plucked Miller and reliever Juan Then out of Arkansas, plus reliever Prelander Berroa may not be far behind.

Two potential call-ups often mentioned by fans, the blogosphere, and the media as candidates to help the rotation this year are Bryan Woo and Emerson Hancock. Dipoto recently suggested either prospect could pitch in the majors right now. The Mariners currently have the luxury of not needing them.

“The pitching that we thought was pooling up in Double-A has manifested. Miller’s already in the big leagues, the others are off to a terrific start. And they can pitch for any other team in the big leagues almost immediately. But right now, when you have the kind of pitching we have, there’s probably not a direct route for them to be in Seattle anytime in the immediate future.” - Jerry Dipoto

Beyond the promising young starters down on the farm, there are other internal options the organization could potentially turn to in a pinch. Darren McCaughan and Tommy Milone are examples of such players.

We’ve already seen the 36-year-old Milone make a start in Seattle this year. McCaughan has one relief appearance with the Mariners in 2023. But he’s been starting games with Tacoma this season and started a contest with the big-league club in 2021.

A strength until it isn’t

Some fans may view Seattle’s rotational depth as an embarrassment of riches. An asset that should be used to add a bat via trade this summer. True, the starting pitching situation looks great today. But it could quickly change in a bad way. To see what I mean, look at the last three World Series winners.

The Astros are, once again, on the rise in the AL West. But the team currently has three starters on the shelf with injuries: Lance McCullers Jr., José Urquidy, and Luis Garcia.

McCullers has yet to pitch this season, is expected to return around the All-Star break. It’s important to note the right-hander has made 25-plus starts just once (2021) since debuting in 2015. Last season, he started just eight contests. Urquidy (shoulder) also projects to return sometime in July. Unfortunately, Garcia is lost for the season after undergoing Tommy John surgery.

Rookies Hunter Brown and J.P. France have stepped in to fill the void created by injuries. Brandon Bielak has also helped. But Houston lacks further depth behind the names we’ve mentioned. Another starter going down or becoming ineffective could have a cascading effect on both the starting staff and bullpen.

Since Opening Day, the Braves have seen Max Fried (strained forearm) and Kyle Wright (shoulder) head to the IL. The organization is also without Ian Anderson (Tommy John surgery).

As a result, Atlanta has been scrambling to field a full rotation recently. But a measure of relief is on the way. Michael Soroka, who hasn’t pitched in the majors since 2020 due to a pair of ruptures of his right Achilles and multiple surgeries, may return this week.

The Dodgers, viewed by many as the preeminent organization in baseball, are experiencing a pressurized situation with their rotation.

As with the Braves, Los Angeles has been challenged to maintain its rotation after a surge of injuries. In recent days, the club lost Dustin May (flexor strain) and Julio Urías (hamstring). Other starters currently sidelined include Michael Grove (groin) and Ryan Pepiot (oblique).

Seller beware

If it appears I’m attempting to scare fans in favor of trading starting pitching, I am. Drawing on the strength of an organization to address an area in need makes sense. But consider this: young, controllable starting pitching is baseball’s rarest commodity.

Some might argue the Astros, Dodgers, and Braves are managing to win despite the injury losses we just discussed. Fair point, although these organizations have been hesitant to trade starting pitching equity in recent seasons and are still on the brink of running out of starters.

In the last 15 months, Seattle has dealt Justin Dunn, plus minor-league starters Levi Stoudt, Adam Macko, Brandon Williamson, and Connor Phillips to land Castillo, Eugenio Suárez, Jesse Winker, and Teoscar Hernández. On top of that, the team has lost Robbie Ray and Easton McGee to Tommy John surgery this year.

Perhaps management taps into the pitching well again to improve this year’s roster. But in closing, I’ll offer the following words of advice for fans advocating a summertime arms deal by the Mariners.

Be careful what you ask for.

My Oh My…