Authors Note: George Kirby had a very memorable rookie season, one that deserves a second look. Consider this article “part one” of two - next time, we’ll do a deep-dive into some analytics and pitch data and talk about dumb stuff like RV/100 and active spin.
Between June 3rd, 2019 (when he was selected 20th overall by the Seattle Mariners) and May 8th, 2022 (his first appearance in the big leagues), George Kirby’s billing had changed significantly. 2018/2019 Kirby carried a reputation of being a soft-tosser, albeit one with a pinpoint fastball and clean mechanics that would likely carry him towards a relatively high-floor, mid-to-back-end starter-type future. Generally, it was thought that the lack of plus secondaries limited his ceiling.
“Kirby represents a safe prospect with a high floor, but lacks for loud tools.” - Baseball Prospectus, June 2019
“He will have to continue to refine his secondary stuff, but he has all the makings of a mid-rotation starter who can get to Seattle in a hurry.” MLB.com, 2020
On Kirby’s ceiling: “If you had to ask me today, I’d say Mike Fiers,” a scout told Joe Doyle, then of Lookout Landing.
A change was set in motion, though, at the Mariner’s cutting-edge high-performance camp in the 2019 offseason at the team’s Arizona complex. Here, the Mariners staff focused on a combination of strength/flexibility training, biomechanics, and mental skills for a select group of prospects, including Kirby.
By early 2022, the language used around him had dramatically shifted. The low-90’s fastball was now sitting 96-97 and touching 102. The previously-middling secondaries were developing some serious bite.
All of this, combined with maintaining his seemingly-perfect command of this new, high-octane fastball, upgraded his profile. No longer was Kirby merely a safe bet to occupy the four-spot in a good rotation, but a prospect who now occupied rare air in the eyes of evaluators.
“I certainly don’t take this lightly: but if I were to pick a minor league pitcher that could ascend to the level of Max Scherzer, it’d be George Kirby.” -Prospect Digest, 2022
‘“Multiple evaluators from rival teams have pegged Kirby as a top-of-the-rotation starter, thanks to his combination of athleticism, stuff and command. “His stuff is explosive, and beats hitters at the top of the zone,” one scout said. “I have him at the top of the rotation with a unique power and precision package.”’ -Baseball America, 2021
Kirby’s sterling rookie season shows that this ambitious ceiling (Max Scherzer??) is very much within grasp. He finished sixth overall in the AL Rookie of the Year award voting and tops among rookie pitchers. If the MLB were like the NFL and had a Rookie Player of the Year award and a separate Rookie Pitcher of the Year award (they 100% should), there’s no doubt Kirby would have been first in the AL.
George Kirby vs. League Average
Being teammates with the crown prince of Seattle and runaway Rookie of the Year winner, Julio Rodríguez, it is probably easy for baseball fans and media to overlook Kirby. To be fair, Julio tends to outshine almost everyone he’s around - a natural byproduct of his easy charisma and loud tools.
However, Kirby also put in a dominant season of his own, one that both provided Seattle a needed boost this year and also inspires confidence that further improvement is on the horizon, that Kirby may he have another breakout season in him.
After a slow start in spring training (and also due to Matt Brash pitching his brains out), Kirby started the season in AA. He wasn’t there for long - after dominating the poor batters of the Texas League and Brash’s struggles on the big league club, he was promoted quickly.
According to Kirby, he certainly didn’t feel settled in right away, though a stellar debut (6 IP, 0 R, 0 BB, 7 K) might tell you otherwise. Beyond the usual challenge of facing batters with better approaches at the highest level, he found himself tested by other realities of life in the majors.
“The travel was the biggest surprise,” Kirby said. “It’s a lot coming in. I was pretty damn tired all the time at first. You just have to change how you recover, and get your sleep.”
That fatigue may have contributed to some inconsistency in the first half of the season. Solid to fantastic starts found themselves interspersed with a few forgettable ones. Overall, his pre-All-Star Break numbers were nothing to scoff at, but the flip really switched for him after the Midsummer Classic.
Kirby first half vs. Kirby second half
|Pre All-Star Break||3.78||107||19.3%||0.313|
|Post All-Star Break||3.02||48||21.6%||0.249|
These numbers are, frankly, insane. A .249 xwOBA would have been the best in the majors for a starter if it were a full season. Small sample size pitfalls allowing, of course, but there’s no doubt that his season was drastically different in the second half. Kirby went from looking like a quality rookie pitcher doing really well for his debut season to a dominant pitcher who owned the league.
When talking about his season, two things stood out as sparking his second-half success. First, he references that fatigue and adjustment. In fact, just prior to the ASB, the Mariners sent Kirby down to Tacoma to throw a short start, essentially a competitive BP session to keep his arm moving.
“I definitely recovered better as the season went on, and I got used to the five-man rotation, but after the All-Star Break, I came back really sharp. I was recovering better than I had,” Kirby said. “I’ve also made some valuable changes in my arsenal that have paid off,” he added.
In the first half of the season, he was throwing the same mix he had in his minors career to date: a fastball, a changeup, a curve, and a pitch that Baseball Savant called a cutter, but Kirby thinks of as a hard slider. Then, right around the midseason break, Kirby came back with a couple of changes. For one, he added a two-seam fastball with a healthy amount of arm-side break to the mix.
George Kirby, Pretty 93mph Two Seamer. pic.twitter.com/giDUTQYClp— Rob Friedman (@PitchingNinja) September 11, 2022
If a new two-seamer unlocking a new gear for a Mariners pitcher sounds familiar, it isn’t a coincidence! It was well covered in the past that Robbie Ray saw a mid-season revival by adding a two-seamer.
“I saw [Robbie] was throwing it, so I literally asked him how he was holding it, I made some changes to make it more comfortable for me and just went with it,” Kirby said.
This two-seamer gave Kirby a legit fifth pitch, and one that is legitimately dangerous, especially thrown glove-side. The deceptive run, along with his ability to paint fastballs wherever he chooses, makes for a deadly front-door pitch.
George Kirby on his two-seam fastball, which he used for three very different strikeouts tonight:— Daniel Kramer (@DKramer_) September 11, 2022
"Being able to front-hip it on guys is probably the best feeling. I've been working on it a lot, so it's good to see that it's really paying off." pic.twitter.com/GaqKFbfcUT
He also tinkered with his slider during the layover.
“I wanted more total movement with it, so I changed my grip. It works well with the two-seam,” Kirby said. “They tunnel really well.” (This is also something we will dig into next time!)
Here’s an example of the early-season slider at 88 mph:
George Kirby, Vicious 88mph Back Foot Slider. pic.twitter.com/q5Vw2e26bo— Rob Friedman (@PitchingNinja) June 1, 2022
And the later season slider, with more sweep and a few ticks slower:
George Kirby, Nasty 86mph Slider...and Sword. ⚔️ pic.twitter.com/5lryKP085H— Rob Friedman (@PitchingNinja) August 13, 2022
The difference might be hard to see with the eye, but it’s not hard to see the difference in the numbers: a .393 xwOBA before the All-Star Break vs a .236 after the break.
The adaptability and flexibility in this stage of his career in his repertoire and game plan is what impresses Ray the most about his rookie rotation-mate.
“He’s not scared of change, he does a good job at changing with the situation, reading the situation and being able to adapt to it,” Ray said. “He can read the game and know when something needs to change, whether it was adding the 2-seamer, or if the four-seam is playing and all of a sudden it’s not, he knows when he needs to alter his game plan. For a guy in his first year, you don’t ever see that. It’s really impressive.”
Kirby certainly impressed plenty throughout the season, especially once the two-seamer/new slider combo was kicking. Here’s one of his best outings of the year, an August day game against the Washington Nationals where he put up seven scoreless innings, giving up no walks and striking out nine.
This clip shows Kirby at his absolute best—getting strikeouts with all of his pitches, but his plus fastball is doing the bulk of the work. Both of his fastballs are located exactly where they’re most effective, with the four-seamer living at the top of the zone and the two-seamer running back into the plate. The slider with more movement and the curveball are both flashing plus here, too. Four plus pitches typically means that you’re going to be close to un-hittable if you can command them.
He set the MLB record for most strikes to start an appearance in that game, with 24. This start had a heavy hand in Kirby earning the August Rookie of the Month award. Please read those stats in the image, because they’re bonkers.
When we spoke before the playoffs had started, though, Kirby said that the thing he was most proud of from his rookie year wasn’t a particular start or stat; it was his durability.
“Definitely [most proud of] throwing over 70 innings, that’s for sure, I’d never done that before. I’m just glad I could stay healthy and stay on top of my recovery,” he said.
However, it’s easy to imagine his performances in the drought-breaking postseason run are a highlight, another impressive feat for a rookie.
Given the way the season ended, it’s might be easy to forget that it was Kirby who went out to close the game down in Game 2 of the Wild Card series against the Blue Jays, trying to hold on to an incomprehensible comeback. Called on in what was surely the highest-leverage situation of the season, Kirby delivered.
It’s also easy to forget that Kirby pitched his socks off in Game 3 of the ALDS at home, pitching seven scoreless innings and also only a third of the game in that marathon of a game. He handled the atmosphere (which was wild) like a seasoned veteran, staying composed and working himself out of several jams to keep Seattle in the game. Despite facing an elite lineup, he stuck to his game plan and executed, over and over again, repeatedly putting down some of the best hitters in the game.
It speaks to the maturity and even-keel attitude that he takes to the mound each day.
“I like to be as chill as possible,” Kirby said of his approach on the mound. “I take the time in between innings to focus on my breath and try to calm down. It’s really tough to do when your heart rate is up the whole time.”
It’s a trait that will lead him to future success - as does his advanced feel for pitching in general, Ray said.
“He has unbelievable feel for all of his pitches,” Ray said. “He doesn’t walk guys, that goes hand in hand with the feel and command he has. I admire that.”
Playing this next game can be dangerous, but I’m going to do it anyways! Playing off of the Max Scherzer comparison in the above “top-of-the-rotation” evaluations, it’s worth noting (maybe!) that it took Scherzer until his fourth full season to record a FIP- or K-BB% better than Kirby’s this year. The same is true for Justin Verlander, and Sandy Alcantara is still yet to best Kirby in those numbers.
In fact, here’s a list of players that threw 130 or more innings with a better FIP- and a better K-BB% than Kirby last season:
Spencer Strider, Kevin Gausman, Shohei Ohtani, Carlos Rodón, Justin Verlander, Aaron Nola, Max Scherzer and Zach Wheeler. Just eight.
Of course, Kirby benefits greatly in these statistics in particular from his stellar, mind-blowing command numbers. But that’s sort of the point of pitching, and it’s what gave Kirby that high floor to start with before the nasty stuff appeared - if you can limit free passes and make the other guys earn every on-base opportunity, you’re going to limit the runs they can score off of you.
The challenge for Kirby next season will be to maintain these strong numbers as hitters adjust to him, and over a larger workload. If he does, there’s a good chance that it won’t just be Julio bringing home some hardware for the Mariners for years to come.