Mariners Starting Pitching to Thank for Place Atop the AL West

It's no secret that the Seattle Mariners boast some of the game's best pitching. Their starting rotation has carried them to the top of the AL West.

NEW YORK, NEW YORK - MAY 23: Luis Castillo #58 of the Seattle Mariners in action against the New York Yankees at Yankee Stadium on May 23, 2024 in New York City. The Yankees defeated the Mariners 5-0. (Photo by Jim McIsaac/Getty Images)

The Seattle Mariners are a team built on pitching. It has been that way over the last couple of years and it remains true in 2024. When their pitchers are on their game, the club more often than not finds themselves in the win column. 

Seattle’s offense, meanwhile, has run into its share of problems in the first two months. They rank last in the league in Strikeout Rate, 22nd in WRC+, 26th in OPS and 29th in batting average. 

The Mariners have several of their expected anchors of the lineup significantly underperforming and have just four qualified players with an OPS over .700. All in all, they have struggled to get into any sort of rhythm through the first two months. 

For most teams across the league, offensive production like this would weigh them down and take them out of contention. In fact, the five teams below them in OPS (Reds, Pirates, Nationals, Marlins and White Sox) are all at least five games under .500 with the Marlins and White Sox well out of playoff contention.

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For Seattle, this has not been the case.

Sitting at 35-28 with a firm grip on first place in the American League West, the Mariners arguably have the best rotation in baseball with each arm possessing the ability to carry the ballclub on any given night.

Their starting pitching unit ranks top ten in ERA, FIP, xFIP and fWAR while being the best in the league at limiting walks (1.98 B/9). Long story short: they have been overpowering.

Let’s break down what makes this group so special.

Bryan Woo And Bryce Miller Have Taken Big Steps Forward

Last year Bryce Miller and Bryan Woo, each in their rookie seasons, had their flashes that showed who they can be as pitchers when they were on top of their game. But they had their growing pains as well, particularly in the second half. 

Each of them had their ERAs sit over 4.50 in the latter half of 2023, and most notable each of them got destroyed by southpaws last year. Opposing left-handed bats posted a .928 OPS for the year against Woo while they held a similar .917 OPS off of Miller.

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Each of them understood that they would need to find something to neutralize lefties. And that they did. A large reason for Woo’s 1.30 ERA and Miller’s 3.18 ERA on the year.

Miller went into copycat mode this offseason, following in the footsteps of fellow pitchers George Kirby and Logan Gilbert by adding a splitter to his arsenal over the winter. And so far it has more than lived up to the hype. Opponents are slugging just .219 against Miller’s splitter with a Run Value of four through the first two months (per Baseball Savant).

Woo’s bread and butter are his two fastballs, each of which are absolutely filthy and have transitioned seamlessly into year two. But there has been an uptick in his changeup usage through his first five starts of the year. And it has spit out a positive result. 

Woo is still throwing his fastballs over 70% of the time as he did in 2023, but he is throwing his changeup 9.3% of the time, which is the secondary pitch he is now most heavily leaning on. For reference, he tossed his changeup 3.7% of the time last year which was used the least of his five pitches.

The results? Hitters are putting up an .077 batting average against Woo’s changeup. That seems like a plan well-executed.

And against left-handed bats? They have a .637 OPS to show for themselves against Miller and a measly .422 OPS against Woo.

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Logan Gilbert Has Been A Force

Gilbert has also taken a step forward in his fourth big league season. In April he was firmly in the Cy Young race after flashing a 2.03 ERA over his first six starts. While May featured one blow-up start against the Twins, Gilbert still sits at a 3.12 ERA.

Gilbert is still very much in the conversation to earn his first All-Star nod of his young career, which in part is thanks to him giving up severely less hard hit baseballs in 2024 along with getting a significant uptick in swing-and-miss. Gilbert was in the 11th percentile in HardHit% a season ago, now he’s in the 63rd. His Whiff% has jumped nearly 20 percent, from the 52nd percentile to the 70th.

The addition of a cutter this season has allowed Gilbert to add a sixth pitch to his arsenal, which he now throws the third most within his arsenal behind his fastball and slider.

Speaking of his slider, it is now his best pitch for the second consecutive season. Opponents are hitting just .207 against it.

Gilbert will need to minimize blow-up starts and keep his HardHit% down over the course of the year. If he does, he has as good a chance to finish top five in the Cy Young voting as anyone in this rotation.

Luis Castillo Is Unfazed

Luis Castillo got roughed up for four earned runs in each of his first three outings of the season. Since then, he has a 2.01 ERA with opponents hitting less than .200 against him.

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While he was one the merchant of an elite changeup, Castillo has transformed as his career has pressed forward. For the third year in a row, his four-seam fastball continues to be an elite pitch. Hitters don’t catch up to it and it is also his primary put-away pitch.

He has also not allowed more than two earned runs in an outing since his third start of the year. Castillo continues to be a big-game pitcher, and all in all is still looked at as the ace of the roster.

Final Thoughts on Mariners Rotation

It cannot be stressed enough the importance of dominant starting pitching. When Kirby has been the worst starter of the five, with very little concern that he is going to level up to his usual self sooner rather than later, it is a nightmare in every series for the opposition. There are no off-days and no weak spots in the Mariners rotation. Every night, teams are getting a headache of a matchup.

Which it why it is so critical that the Mariners secure themselves a postseason bid. If they simply get into the field, their rotation can take them the entire way. That’s how good it is.

They may add an impact bat at the trade deadline, and the importance of Julio Rodriguez returning to his elite form is crucial, but the backbone of this roster is the starting pitching. They live by it and die by it. And it is the reason they sit with a comfortable lead atop the AL West.