Solving George Kirby

George Kirby's next step is a bit of a puzzle.

We’ve never seen anything quite like George Kirby. I mean that literally. His reputation precedes him but it somehow doesn’t do him justice. Since integration, no one with at least 40 career innings has a lower walk rate. To put that into perspective, that’s a sample of 5072 pitchers. 40 innings is not a large amount, that includes some real outlier types who only pitched in a handful of games and weren’t good, but at least they made hitters work for it. And still, none of them can best Kirby’s 3.0 BB%. Nearly 80 years of Major League Baseball, the way the game has changed over all that time. None compare to Kirby.

He does this while having what is undeniably upper-echelon stuff. He’s not just lobbing 86 mph sinkers into the zone and hoping for the best. He sits 95 with his fastballs. He has a deep group of secondary pitches. With that said, would you consider Kirby among the top tier of aces in the league today? He’s very very good, there’s no arguing that, but would you say he’s a top 5 pitcher in the game when everyone’s healthy? Top 10? What’s stopping him from reaching that tier? To get a better idea of the type of pitcher we’re dealing with, let’s look at what he has to offer.

The 4-Seam

Kirby’s arsenal is led by his 4-seam fastball. As previously mentioned, he throws it hard, averaging 95.6 mph and maxing out at 99.3 mph this season. Its shape is almost exactly league-average. It has 16.1” of iVB, 9.1” of HB, and comes from a generic release both vertically and horizontally. His release extension is also average.

Ordinarily, it would be a bad thing to have a pitch this close to the league average. The only things that stand out about it from a stuff perspective are that it’s 1.1 mph harder than the league average 4-seam, and has 1.7” more run. Yet this pitch performs well for Kirby night in and night out due to his stellar command of it. 

He operates with surgical precision, peppering the top of the zone, as well as above it. His absurd 42.9% O-Sw% leads all starters this season. Hitters generally don’t hit pitches out of the zone well, and Kirby gets hitters to try that against his fastball better than anyone else. This also allows him to miss bats at an above-average clip.


The Sinker

Kirby’s other fastball is thrown with the same velocity as his 4-seam but comes with a different shape. This one has 11.4” of iVB, and 15.9” of HB. In a vacuum, this isn’t particularly impressive. However, the way it fits into Kirby’s arsenal makes this an excellent pitch. It spins on the same axis as his 4-seam, and he does not modify his release point for it. Hitters have no way of telling which of his fastballs is coming if they even can identify that it is a fastball. Suddenly, having to guess between two pitches that are separated by 4.7” vertically and 6.8” horizontally becomes a major problem.

Kirby fills the zone with this pitch at a high frequency. Despite showcasing the ability to locate it at the back door (glove-side), he doesn’t get a ton of called strikes with it. This is because hitters expect this pitch to wind up in the zone due to the scouting report on it. Unfortunately for them, that opens up his 4-seam to fool them and swing under it when it’s above the zone.

Beyond that, he can also run his sinker in on the arm side, tying up right-handed hitters, and occasionally getting lefties to chase it out there. The way his fastballs work in tandem is why it’s acceptable that he throws them a combined 59% of the time. They’re such a good pair that open each other up for success.


The Slider

Kirby’s slider is troubling, everything about it seems great until you look at how it’s performing. It comes in with good velocity at 86.7 mph. More importantly, it has tremendous depth and movement with -2.9” iVB and 8.3” HB. Getting negative iVB on a breaking ball thrown this hard isn’t particularly common, and there are only 8 pitches with more that are thrown harder. Notably, none of them are thrown by starters.

Adding to the quality of this pitch, its spin direction mirrors the fastballs almost perfectly. The spin activity doesn’t match as well, but achieving the first half can add to the pitch’s deception. Despite this, it doesn’t live up to its potential. He zones it consistently, but it’s gotten hit well on contact this year. I believe this is mostly due to where he’s throwing it in the zone. Too many of them are catching the middle of the plate.

Furthermore, for the third season in a row, Kirby’s slider is running a below-average chase rate. I have some theories as to why that is but no concrete answer, unfortunately. When Kirby is feeling his slider, he’s capable of burying it off the glove-side corner where it looks like a strike until it dives down and further to that side. He does sometimes miss the mark and throws it in less tempting locations for hitters. It’s also possible the pitch’s deception is taken away from by how he uses it. With how frequently his fastballs are high, anything coming in lower could potentially just be spit on by hitters, with them assuming it’s a breaking ball. This could be why the slider has an excellent called strike rate. Deception only works to a point, if he’s not tunneling the pitches well, he’s less likely to get those chases. 

These are the difficult questions that can come with pitch design. What do you do when a pitch is underperforming? If it’s because of how he’s using his fastballs, do you dare change what’s working for them? Do you try throwing the slider in a new spot to accommodate them and have to retrain your ability to locate it? Do you accept that the slider may never get as many swings and misses out the zone as it should and just try to keep it low for strikes and hopefully bad contact? None of the answers are perfect. What he’s doing now is working well enough, but it could also be part of what’s keeping him from reaching that next level. He doesn’t have a do-it-all, whiff-heavy out pitch against righties beyond his fastballs.

His slider is excellent, but its fit in his arsenal is questionable. It feels like it could be that dominant secondary that gets him whiffs when he really needs them, but it hasn’t been that to this point. The potential for this pitch is high, but he may need to rework it a bit to get it to its ceiling.


The Splitter

Kirby’s offspeed pitch of choice is a gorgeous splitter. He has 10 mph of velocity separation from his fastballs at 85.5 mph. Perhaps more impressively, it has 16” of vertical movement separation from his 4-seam, down at -0.2” of iVB. This pitch falls off of the table on its way to the plate. When a hitter is expecting a fastball, a splitter that drops like this should be nigh unhittable. It only has 8.9” of HB, which is low for an offspeed pitch, but with this much depth, it doesn’t matter much.

There is, sadly, a problem holding this pitch back from being what he wants it to be. It just doesn’t seem to be fooling anyone. It has a shockingly low called strike percentage, a below-average whiff rate, and a below-average chase rate. This is caused by one obvious and one potential issue. His command of this pitch is surprisingly shaky. Too often it finds itself at the bottom of the zone, middle-middle, or too far out of it to be enticing. None of these locations are ideal for this type of pitch.

The other “problem” comes with a speculation disclaimer on my part. I cannot prove this, it’s just a theory that I thought was worth mentioning. I’m not convinced this pitch is particularly deceptive. He replicates his fastball release reasonably well, but the positives end there. There’s a substantial difference in spin direction between it and his fastballs. It’s also possible that the exceptionally low spin rate it has could be a tell of sorts. The sample of pitchers with offspeed pitches that spin this little is small, but the ones that do manage to achieve average or better chase rates all have at least one thing going for them that Kirby doesn’t. They either locate the ball well by throwing it directly below the zone, they have spin directions that are closer to their fastballs, or they have both.

In Kirby’s defense, this is a new pitch for him. He only started throwing it in 2023. My hope is that with time his command of it will improve and he’ll find a way to locate it well below the zone so that its deception matters less. In the meantime, it’s an acceptable if underperforming pitch he can use against opposite-handed hitters.


The Curveball

Like his other breaking ball, Kirby’s knuckle-curve is a pitch that looks excellent on paper but its actual effectiveness is a bit less than you’d want. He throws it with power at 82.7 mph and gets a good amount of movement at -13.9” of iVB, and 9.5” of HB. As a bonus, this pitch creates an even better spin mirror to his fastballs than his slider does. Even further, it can work in tandem with his slider as they spin on the same axis but move differently.

What should be an excellent secondary has not lived up to that expectation for him this season. Previously it performed well enough because he was zoning it consistently and getting called strikes with it, with some chases and whiffs as well. The drawback was when he missed in the zone with it, it was getting smacked by hitters. This year, he seems to have lost his ability to throw good strikes with it. It’s either in the middle of the zone or out of it entirely. The ones outside of the zone have been solid and they still garner chases and whiffs. It’s still worth throwing, but I’m puzzled as to why it’s fallen off the way it has.


The Cutter

This is a new pitch Kirby gave a trial run for two starts in May this season, so he’s only thrown 10 of them. The shape across those 10 has been pretty consistent so I feel reasonably confident that the movement metrics will hold if he brings it back. He’s been throwing it 92.1 mph with 8.6” of iVB and 1.5” of glove-side HB. This is theoretically a solid addition to his arsenal if he can locate it on and off the edges. It could potentially open up his slider to more chases, a previously noted problem for Kirby. If that’s the idea behind it, it would explain why he’s thrown all but one of them to righties. I like the concept of this pitch at least, even if it’s probably liable to get crushed on contact.


The Outlook

Where does this leave us? Kirby has two difficult paths to progression as a pitcher in front of him. One is a bit simpler though by no means easier. Sharpening the command of his secondary pitches would go a long way to improving their performance, especially the splitter and curveball. Kirby’s relentless tinkering as a pitcher and dedication to growth inspire confidence that this could be doable for him. He’s already got generational command of his fastballs and an all-time ability to avoid walks. It’s important to remember that Kirby is just 26 years old with only 401 MLB innings. He’s still developing as a pitcher. This is unlikely to be his final form. Betting against his ability to improve his pitches seems foolish.

The other path presents philosophical questions about his pitch design. Messing with his fastballs is likely a bad idea, so what else can be done with his arsenal? He could focus on that new cutter with the goal of getting his slider to play up to its potential, but that could take away from the development of his other pitches.  On the other hand, it could also improve his fastballs even further. Pitchers who throw a mix of 4-seams, sinkers, and cutters tend to play above their stuff quality due to how they work in tandem.

He could also tweak the strategy behind his slider and throw it higher in the hope of tunneling it with his fastballs a bit better. That could lead to more chases, but waist-high sliders come with the risk of hitters getting under them and hitting them better than they would if they were lower.

It’s very difficult to know which option is the most viable as an outside observer. The one that sees him improving without changing what he’s doing strategically is the easiest to picture, but it’s simple to say: “He’d be better if he located his pitches better”. Reading it back that feels like an insane thing to say about Kirby but it’s true. Maybe that’s holding too high of a bar though.

That leaves the pitch design tweaks, which are purely speculative as I’m not there in the lab with him. Kirby’s shown a willingness to modify what he’s doing as needed. His arsenal has changed pretty drastically since being called up. I wouldn’t be surprised if more changes are coming assuming he doesn’t take the next step forward from a skills perspective. He may do that anyway in his endless pursuit of improvement.

The tone of this article has been unintentionally negative since the end of the sections about his fastballs. In his current state, Kirby is an excellent pitcher who can thrive on his fastballs alone and his cast of secondary pitches to support them and keep hitters honest. I don’t want to lose sight of that. We’re talking about an exceptionally talented individual who is already in the conversation as one of the best starters in the game. I’m pointing out his flaws with the confidence that if he can solve even one of them, his game will be substantially elevated. There’s another level to his pitching that he hasn’t unlocked yet, I’m certain of it. How he solves the barrier preventing him from reaching it is up to him, but he’s given me no reason to believe he can’t.

Jack Foley

Jack is a contributor at Pitcher List who enjoys newfangled baseball numbers, coffee, and watching dogs walk by from the window where he works. He has spent far too much time on the nickname page of Baseball-Reference.

One response to “Solving George Kirby”

  1. TJ says:

    Great article, thanks! Love watching Kirby do his thing and appreciate the deep dive. Feels like his curveball can do more damage than it’s currently doing – thought being: wouldn’t that tunnel better with his 4-seam (maybe more-so than the slider)?

Leave a Reply

Your email address will not be published. Required fields are marked *

Account / Login