The Dominance of George Kirby

All stats through Wednesday's games.

The Mariners have developed into one of the best organizations in baseball at developing pitching, especially college arms. Their 2018 first-round draft pick Logan Gilbert has the seventh-best WHIP in baseball, the 24th-most strikeouts, and the 18th-best BAA, at .231. In 2020, they drafted Emerson Hancock, who just arrived at the big-league level after performing well in the minor leagues. But it's the pitcher they took in between that has made the biggest impact on the biggest stage, and that's George Kirby. Drafted in 2019 with the Mariners' first-round selection, Kirby was ranked 18th overall among a draft class that included Adley Rutschman, Bobby Witt Jr., and Corbin Carroll. Kirby led D1 pitchers with a 17.83 K/BB in the 2019 season at Elon, and that was just a preview of what was to come for Kirby. He tore up the minor leagues, striking out 139 batters in 117.1 innings pitched with a 2.61 ERA. And when he arrived at the big-league level, Kirby never looked back.

Consistent dominance

No pitcher in baseball this year has thrown a quality start (defined as going at least 6 innings and allowing 3 earned runs or fewer) more often than Kirby has. Kirby leads MLB pitchers in Quality Start Percentage at 73.9%, just ahead of Gerrit Cole and Logan Webb. And what enables him to do this? He's remarkably efficient, enabling him to work deep into ballgames. Kirby averages 14.88 pitches per inning pitched, which is the 8th-fewest out of all qualified MLB pitchers. He accomplishes this by working ahead in the count. Kirby has the 4th-best first-pitch strike rate in all of baseball, at 68.5%. Throwing first pitch strikes allows Kirby to work deep into ballgames while keeping runners off the bases and runs off the board. When Kirby toes the rubber, he gives you a bigger chance of a good outing than any other pitcher in baseball. Not to mention, he can give a bullpen an extra night of rest. Look no further than his last start against the Baltimore Orioles: 9 IP, 3 H, 0 BB, 7 K. Kirby has thrown the 14th most innings in baseball this season, and they have been good ones.

Best fastball in baseball

Pitchers will tell you that the most important pitch is a well-located fastball, and nobody in baseball does that better than George Kirby. The shadow zone is basically the edges of the plate; it's not the heart of the plate, but it's not a pitch that will never get called a strike, either. It's that part of the zone where you always find yourself yelling at the TV because the umpire missed a call there. And it's where pitchers make their money, because likely either the batter freezes and it's a called strike, or the batter can't make strong contact. Among all hitters who have seen at least 1,500 pitches this season, their wOBA on pitches in the shadow zone is .286, which is significantly below that group's overall wOBA this year of .338.

Percentage of four-seam and two-seam fastballs in the "shadow zone"

1. Justin Steele, CHC - 30.1%

2. George Kirby, SEA - 29.7%

3. Jake Irvin, WSN - 29.1%

4. Patrick Corbin - 28.8%

5. Joe Ryan - 28.2%

Kirby is second-best in baseball at throwing his fastball in the shadow zone, only behind the man with the 2nd-best ERA in the National League in Justin Steele. For a visual example, take a look at the graphic below, showing the fastballs Kirby threw in his July 6 start against Houston.

Kirby thrived on the edges of the plate, especially at the top of the zone, and left almost nothing out over the middle of the plate where the Astros' hitters could do damage. As a result, he (because of course he did) threw a quality start, going six innings and allowing just one earned run.

The remarkable thing about Kirby's fastball is not that not only does he have very good command of it, but it's a filthy pitch. He throws the 7th-hardest fastball in baseball, averaging 96.1 MPH with wicked movement, and when he pairs that with his command, his fastball is pretty much unbeatable.

Sports Info Solutions Fastball Runs Above Average

1. Zack Wheeler, PHI - 19.6

2. Zac Gallen, ARI - 19.4

3. George Kirby, SEA - 18.1

4. Luis Castillo, SEA -17.9

5. Gerrit Cole, NYY - 17.7

His completely absurd strikeout to walk ratio

George Kirby attacks the zone like no one else in baseball. His K/BB ratio is an astounding 9.36, as he's struck out 131 batters and walked just 14. This isn't just the best of any pitcher in baseball by a long shot, but it's also historically good. Kirby's 9.36 K/BB this year would be the 5th best a pitcher has had since 1920, and the best since Phil Hughes in 2014.

Best K/BB% by qualified pitchers since 1920

1. Phil Hughes, MIN - 11.63 (2014)

2. Bret Saberhagen, NYM - 11.00 (1994)

3. Cliff Lee, SEA/TEX - 10.28 (2010)

4. Curt Schilling, ARI - 9.58 (2002)

5. George Kirby, SEA - 9.36 (2023)

He's able to do this for the reasons already discussed; pinpoint command, working ahead in the count, and having a great fastball. But he's not just limiting the walks. He's also striking hitters out, due to a high quantity and quality of secondary pitches. Kirby throws five pitches more than 4% of the time, and the highest wOBA that hitters have against any of them is .300, on his slider. Kirby's splitter and curveball have been especially effective, because he's been able to get whiffs down in the zone where hitters can't do much damage.

While his fastball has been key to his success this season, his secondary pitches have enabled him to have a chase rate in the 81st percentile and be one of the best pitchers in baseball.

George Kirby has a solid case for AL Cy Young Award winner this season. Powered by his remarkable ability to pound the zone with high-velocity fastballs and devastating secondary pitches, as well as his ability to work deep into games, he has blossomed into one of the best pitchers in baseball in his sophomore season. Take a look at where he ranks among AL pitchers in the following categories:

WHIP - 1st (1.00)

K/BB - 1st (9.36)

fWAR - 3rd (3.1)

ERA - 5th (3.11)

IP - 7th (144.2)

If Kirby continues like this, the Mariners look like they have a homegrown Cy Young-worthy pitcher on their hands not just this year, but for years to come.