By Jonah Drew

The Seattle Mariners rotation had high expectations coming into 2024 and they have lived up to expectations. They currently sit at 5th in rotation ERA with a 3.42 but it’s clear they are even better than that. Due to some unfortunate injury luck and some frankly out of body stretches from pitchers in the Top 4, that mark would tell you this is not unequivocally the best rotation in baseball. This just not true, there is no five in baseball that can hold a candle to the group of Castillo, Kirby, Gilbert, Woo, and Miller. Considering the age and sustainability of this quintet, it is not crazy to say that they have the chance to be an all time starting rotation. Let’s get into the breakdown of each of their respective individual brilliance.

Luis Castillo

Starting with La Piedra, Castillo was acquired at the 2022 Deadline from Cincinnati in exchange for high profile infield prospects, Noelvi Marte and Edwin Arroyo. Since landing landing in Seattle, Castillo has carried his Midwest dominance and more with him. Castillo finished 5th in Cy Young voting with a 121 ERA+ across a league leading 33 Starts in his first full season in teal. 2024 has been more of the same has Castillo has not missed a start and has posted a 3.35 ERA. Castillo’s K/BB ratios continue to be impressive as he has posted a 25% K rate with just a 6.7% BB rate. Since the trade, Castillo has made a tangible effort to increase his fastball usage. Castillo now throws his 4 seamer 46% of the time compared to just 32% of the time in 2022 and it seems to be paying off. His fastball has been by far his best pitch with a +11 Run Value and a .289 xwOBA. Despite being the “Ace” of this rotation, analytically speaking, there is a real argument that Castillo is not even in the Top 3 of his own team. That is not an indictment on Castillo rather it is an effort to shower praise on his elite rotation mates.

George Kirby

George Kirby is an absolute anomaly in today’s baseball landscape, there is just nobody like him anymore. Since the turn of the century there have been 4 pitchers to post a BB/9 below 0.900(In a Full Season). Carlos Silva in 2006, Phil Hughes in 2014, Cliff Lee in 2010 and you guessed it, George Kirby in 2023. This helped Kirby finish 2023 with a 3.35 ERA, although the mark has taken a slight dip, a 3.81 is nothing to scoff at, especially when the peripherals are much better. Kirby sits at a 3.36 xERA and a .293 xwOBA. Kirby has kept up his uncanny strike throwing ability while also generating more swing and miss than ever. Kirby is at a career high 24% K rate while walking an ungodly 2.1% of batters. Kirby is also consistently inducing weak contact, something that has not always been the case. Kirby is allowing an average exit velocity of 88.0 MPH(68th Percentile) and a 35.7% hard hit rate(70th Percentile). George Kirby on a planet of his own in terms of pure control.

Logan Gilbert

Since Gilbert made his big league debut back in 2021 he has quietly been of the most consistent arms in the game with his best season coming in 2022 where he posted a 3.2 ERA across 185 innings. However, 2024 looks to be ready to surpass that if he can continue similar production. All signs point to that being the case as he currently sits at a 3.38 xERA and a .294 xwOBA. Gilbert is very well rounded as he generates swing and miss(29.1% Whiff Rate and 24.1% K Rate). The best part of his arsenal is though is the fact that he can do this without sacrificing any control, Gilbert posts a 5.7% BB% which puts him in the 82nd percentile. Gilbert has recently made significant changes to his arsenal that have propelled him into ace territory. His 4 seamer does have a tendency to get hit around a bit so he smartly decreased it’s usage which has helped it play at least marginally better. He debuted his split finger in 2023 and it has been unequivocally his best pitch ever since. The pitch has posted a ridiculous 45% Whiff Rate and a .136 xwOBA. He also debuted both a Cutter and a Curveball, both have which have yielded positive results. His overall arsenal is greatly benefited by his unfair 7.7 feet of extension. Gilbert has transformed himself into one of the best pitchers in the American League.

Bryan Woo

Bryan Woo debuted in the first half of last season and while his 2023 may not have jumped off the page results wise, he showed he had the potential to be a force in this league for years to come. In his rookie campaign, Woo posted a 4.21 ERA across 18 big league starts. Woo has struggled with 2 alarming arm issues already in 2024 but luckily all reports show that Woo is going to be okay and will return in due time. However, for the 6 starts Woo has made in 2024, he has just about set the world on fire. In those 6 starts, Woo has pitched 33.2 Innings to the tune of a 1.07 ERA. The peripherals back it up to, Woo has pitched to a 1.80 xERA, a .188 xBA, and a .215 xwOBA. All of which are marks that land him in the top 5 percentile in all of baseball. Woo also has a remarkable 1.7% Walk Rate and 2.2% Barrel Rate. Yea, I’d say that a recipe for success.

Bryce Miller

It’s crazy to say but Bryce Miller is really the black sheep of this Seattle rotation. For the Mariners to be able to say a 25 year old with a Mid 3 ERA is your “Black Sheep” is a luxury that almost any organization would kill for. Miller and Woo will always be synonymous with each other as they are so similar in a multitude of ways. First off, they are both college arms who debuted for the Mariners in 2023. But the main similarity is the arsenal and specifically the fastball. They both dominate with a high riding fastball that is absolutely dominant at the top of the zone. They have both been holding up their end of the bargain as Miller has been pretty successful in his own right. Miller sits at a 4 flat xERA and a .263 wOBA. Miller has a projectable formula for success as he dominates with the aforementioned 4 seamer and he has an elite secondary with other tertiaries to play off of it. Miller’s split finger is beyond elite has it boasts some of the best individual results of any pitch in the game. Miller also mixes in a sinker, a sweeper/slider, and a cutter to round out his mix. Bryce Miller as your 5 is an absolute gluttony of riches.

Sources

Baseball Reference

Baseball Savant

Fangraphs

The Seattle Times