By Coleman Smith
George Kirby burst onto the major league scene in 2022 to the tune of a 3.39 ERA across 25 starts en route to a 6th place finish in Rookie of the Year voting. With a K-BB% above 20% and a FIP below 3, many were excited to see a full season of Kirby in 2023 to see if he would take a step forward. While the strikeout numbers still aren’t quite there, Kirby was certainly impressive, topping 190 IP while still posting a 3.35 ERA for a Mariner team that would fall just short of another playoff appearance. Heading into this season, Kirby is being drafted in fantasy among the top starters in the league (by ADP: SP10 on Yahoo, SP15 on ESPN). His floor is likely high enough to not disappoint owners, but if he can unlock just a bit more swing and miss he could be in the conversation for the Cy Young award at the end of the year.
Kirby’s savant page is interesting because we can see he is amazing at a couple things and average or below in the rest. His walk rate is amazing, and he gets lots of chases. These chases don’t lead to strikeouts however because they don’t create whiffs. His fastball was standout, and his breaking pitches above average, but his off-speed was poor. His off-speed is being held down by a really bad changeup that he would end up scrapping as we see below. Many expected stats didn’t love him, but 96th percentile pitching run value is certainly nothing to scoff at.
Kirby began the season with the following: 4-seam fastball, sinker, curveball, slider, and changeup. By June however, he would cut out the changeup and add a splitter, a popular move recently among pitchers with poor changeups.
If you’re interested in the changeup/splitter revolution, we just wrote about it here! When comparing the performance of Kirby’s changeup to his splitter, it’s pretty obvious why he chose one over the other.
| AVG | SLG | wOBA | Whiff% | EV | GB% | |
| Changeup | .500 | .900 | .590 | 9.1 | 93.0 | 30.0 |
| Splitter | .143 | .286 | .179 | 35.7 | 90.2 | 41.4 |
The splitter was better at missing bats, creating soft contact, and keeping the ball on the ground. I’ve talked a lot about missing bats, and this is mainly due to how well Kirby already excels at keeping the ball in the strike zone. He had the lowest walk rate in MLB among qualified starters this season at just 2.5%. He also finished 4th in pitches per inning pitched, coming in at just 14.8 and placing right behind Sandy Alcántara. Kirby has elite command, and uses it to attack hitters and get through innings quickly. This allows him to go deep into games, as well as limit big innings by not putting extra runners on base.
Kirby’s command is not just limited to walks, as he also has the highest strike% in the league. His four most thrown pitches all have a first pitch strike rate above 60%, with three of them being above 65%. This ability to control counts and stay ahead of hitters prevents them from getting comfortable in an at-bat and getting a pitch they can drive.
Another area Kirby stands out is his R/L splits. The table below shows just how similarly opposite handed hitters fared against Kirby, not just on batted balls but strikeouts and walks as well. One thing to note here is that in 2022, RHB had a .366 wOBA compared to .245 for LHB, meaning he was a reverse splits pitcher when he came up.
| AVG | OBP | SLG | wOBA | K% | BB% | |
| RHB | .247 | .270 | .388 | .283 | 22.3 | 2.0 |
| LHB | .246 | .270 | .402 | .286 | 23.2 | 3.1 |
Typically pitchers are less effective against opposite handed hitters, in part because their breaking pitches break into the hitter instead of away. The following movement plot is from the pitcher’s perspective, with pitches on the right side breaking into right handed hitters and on the left side breaking into left handed hitters.
One reason the changeup may have struggled is due to having little separation from his sinker. The pink triangles are almost on top of the orange pluses, meaning from a shape and movement perspective these pitches were too similar. By switching to a splitter, Kirby added almost 5 inches of depth to his fifth pitch while keeping the arm side break away from lefties.
While the pitch was hardly thrown to righties, it grew in usage as he gained confidence against lefties. By the end of the season it was his 3rd most thrown pitch to LHB. What excites me so much about this is the pitches performance was exceptional.
In 25 batted ball events (BBE), left handed hitters had zero barrels against the splitter, as well as just four total base hits and one extra base hit. With 2 strikes to left handed hitters, the pitch had a stellar 23.8% swinging strike rate. He threw it in the zone the least of all his pitches, yet still held a strong swing and swinging strike rate. This is his “out” pitch against LHB that he can go to when he gets ahead in the count and wants a swing and miss.
Kirby’s slider is also a notable pitch, mainly for it’s shape and movement characteristics. On the movement plot from above, we see the slider with a pretty wide spread. The pitch has gone through some transformation, changing shape after 2022 and also during 2023. The table below compares the three sliders and how they have fared, showing steady improvement with each tweak made. Kirby’s slider is also his best rated pitch by Stuff+, coming in at 126 and placing it in the top 10 among qualified pitchers.
| Velo | IVB | HB | SwStr% | Whiff% | |
| ’22 Slider | 85.5 | -0.6 | 10.1 | 7.0 | 14.0 |
| ’23 1st half Slider | 85.8 | -2.8 | 11.9 | 6.9 | 17.5 |
| ’23 2nd half Slider | 87.2 | -1.9 | 9.4 | 14.8 | 28.7 |
The pitch is strange because it sits somewhere between a slider and sweeper in terms of horizontal movement, but with depth more similar to a slurve. The one to the right was the slower, sweepier version from early in the season.
The average RHP slider had 1.7 inches of IVB and 6.2 of HB, compared to 1.4 IVB and 14.5 HB for the sweeper.
The ’23 second half iteration, shown to the left, was the most successful and was thrown harder than the average slider, without sacrificing much depth. With this being Kirby’s main breaking ball to right handed hitters, it will be important for this pitch to be successful.
One of Kirby’s big flaws is his time through order (TTO) numbers. It’s typical for a pitcher to get a little worse each time through the lineup as hitters see more of their arsenal and begin to figure out how they want to pitch them. Kirby stays steady the second time through the lineup, but when the third time comes around things go haywire.
| Time thru order | AVG | OBP | SLG | K% | BB% |
| 1st | .229 | .266 | .359 | 24.7 | 3.6 |
| 2nd | .224 | .246 | .354 | 22.0 | 2.5 |
| 3rd | .305 | .314 | .511 | 21.1 | 1.0 |
Interestingly, his strikeout rate drops each time through the order, but so does his walk rate. This may suggest Kirby is trying to attack hitters even more late into games, but this may be hurting him. We talked earlier about how Kirby struggles to create whiffs, but this really starts to bite him as hitters see more of him. By the 3rd time through a lineup, hitters are making adjustments and seeing pitches better than they were early in the game. More pitches in the zone during this time means hitters have more chances to get a hold of one and make Kirby pay. To have success late in games, I think Kirby may have to start biting the edges more and trying to induce soft contact or swings and misses that way. He’s got good enough command that he should be able to keep pitches close enough to the zone to induce swings without getting in too many bad counts. This could be the difference in Kirby pitching 190 innings again in 2024 or throwing 210+ innings. If Kirby can replicate a low 3’s ERA in over 200 innings and get his K% closer to 24-25%, we could be talking Cy Young next season.
Quickly, if you payed attention to the legend on the movement plot shown earlier, you may have noticed a knuckleball. That’s right, Kirby threw one knuckleball this year on October 1st, the day of Tim Wakefield’s passing. After the game, Kirby would confirm that he threw the pitch to honor Wakefield, saying “I loved watching that guy throw, even though he’s a Red Sox player and I’m a born Yankee fan… …But yeah, it was a great day to throw it and I’m glad Seager missed it and didn’t take it deep. So, yeah that was fun.” Take a peek at the knuckle below, and props to Kirby for such a heartwarming tribute.
2024
| ERA | GS | IP | K% | BB% | W | L | |
| Steamer | 3.61 | 32 | 191 | 23.4 | 4.2 | 12 | 10 |
| ATC | 3.55 | 30 | 181 | 23.4 | 3.7 | 12 | 9 |
| Zips | 3.48 | 29 | 168 | 21.9 | 3.9 | 12 | 8 |
| The BAT | 3.72 | 30 | 166 | 22.0 | 4.3 | 11 | 10 |
Projection systems currently aren’t loving Kirby, with all but Steamer expecting a step back in IP and all expecting a bump in ERA next season. I’m not entirely sure what’s up with Zips and The BAT’s IP projections as they have him right at the same number of starts as 2023, yet an almost 25 IP falloff. I think these projections may be weighting 2022 in their IP calculation, but Kirby is 26 and just getting used to a full season workload as a professional pitcher. He threw a total of 156.2 innings between the minors and majors in ’22 and 190.2 in ’23, so I don’t see 200+ innings being an issue.
For fantasy, Kirby’s current ADP sits in the late 30’s to early 40’s on Yahoo and ESPN. Being drafted as a late end SP1, Kirby will likely give you volume but not a ton of strikeouts. The Mariners offense likely won’t be great, so the win projections around 11-12 seem accurate. In points league formats, I think Kirby easily can outperform his ADP off volume alone, with the potential to be one of the best pitchers in the format due to his low walks and ERA. The cost may begin increasing closer to draft day as hype builds, but Kirby has a solid floor and exciting ceiling that make him a great choice early in fantasy drafts. Eno Sarris of The Athletic and Nick Pollack of Pitcherlist are two of the top pitching guru’s in the fantasy scene, and currently have Kirby ranked at SP5 and SP7, respectively. If he can keep improving the slider and splitter, I believe Kirby could cement himself as one of the best pitchers in baseball in 2024.
Coleman Smith is a writer for and co-founder of Low Three Quarter Media. See more of his work and others’ work on the site through the links at the top of the page, or explore another recent article linked below.
Low Three Quarter Media 
Leave a comment