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George Kirby: The Legend Has Only Just Begun

Since posting the highest game score by a pitcher making their MLB debut in Mariners history, George Kirby has shown he’s exactly what Mariners fans hoped he would be.

To say that George Kirby has elite command may somehow actually be an understatement. Kirby finished his college career with a 19-8 record, 3.34 ERA, 50 walks and 258 strikeouts in 240 IP. His career 5.16 K/BB ratio was impressive, but his 17.83 K/BB ratio in his final season was tops in the nation. That impressive control immediately transitioned with him to the minor leagues. In 115.1 minor league innings, Kirby struck out 137 and only walked 20. Good for a 6.85 K/BB ratio. Through his first seven major league starts, Kirby has an impressive 35 Ks and only four walks. That 8.75 K/BB ratio would be tops in baseball once he’s pitched enough innings to qualify. His 0.97 BB/9 would be second. Not bad for a 24 year old rookie.

While the walk stat alone is pretty damn impressive, let’s break down the pitches that make him so effective:

The Fastball:

Oh the fastball. The one pitch hitters dream of seeing, except when Kirby throws it. When he’s locating the pitch, there aren’t many more dominant fastballs in the game. Averaging 95.5 MPH and topping out around 98, hitters are struggling to the tune of a .218 batting average against. His fastball speed is currently in the 79th percentile in all of baseball.

While the speed and pinpoint accuracy of it does play a factor, it’s the amount of movement Kirby gets on the pitch that makes it even better. The fastball breaks 8.3 inches horizontally, 14% more than the average fastball, which has lead to a 25.8% whiff rate and -4 run value. Pretty damn impressive, especially for someone with only seven career starts in the bigs. It’s also by far his best strikeout pitch with an excellent 24% putaway rate.

Much like teammate Logan Gilbert, Kirby is a very fastball dominant pitcher with a very dominant fastball.

The Slider:

The slider is what many are expecting to become his next plus pitch. So far, though, that hasn’t been the case. While it’s had some nasty moments, it’s also been the pitch he’s struggled with the most. At least on paper.

While throwing it 26% of the time, his slider has already been hit around for three home runs and a .366 average. Most of the struggles with it have come via the incredibly low active spin rate. While Kirby doesn’t get the most spin on the pitch to begin with (only 2140 RPM on average), hardly any of that rotation is actually going towards the movement of the pitch itself. In fact, his 35% active spin rate on his slider is one of the lowest in baseball. He gets decent movement on the slider (31 inch vertical drop, 4.4 inch horizontal), but most of that is from gravity itself. The spin rate is only attributing to about 5 inches of the total movement.

The pitch isn’t a lost cause, though. Kirby is still incredibly young and learning his pitches. His slider and low active spin rate actually remind me of a breakdown of Corbin Burnes and his cutter I saw by Foolish Baseball over on YouTube. It’s worth a watch.

The Changeup:

What’s better than a pitcher who throws a 98 MPH fastball for strikes, consistently? A pitcher who also throws a 85 MPH change up that drops off the table for strikes, consistently. Kirby’s changeup is another work in progress, but once he gets it figured out the sky’s the limit. Currently only getting hit at a .235 clip, but the .337 xBA tells a different story. Much of that xBA metric seems to come from a small sample size, though. Kirby’s only thrown it to 17 batters and given up five hits, four of which were for extra bases.

What the changeup really has going for it is the crazy movement it gets. Kirby’s change gets 34.7 inches of vertical drop (10% more than average) and 15 inches of horizontal break (3% more then average). All of this is thanks to its 100% active spin rate despite only generating 1412 RPM on average.

The speed differential and larger than average break have lead to a 21.2% whiff rate. Second highest of all Kirby’s pitches. It’ll need a larger sample size to understand exactly how effective it can be at the major league level, but it has all the intangibles of being a serviceable pitch with plus potential.

The Curveball:

The curveball is Kirby’s lowest graded pitch according to fangraphs, yet it might be my favorite. I’m not sure if it’s lack of confidence in the pitch or what, but Kirby seems to rarely throw it. Through 37 innings, he’s thrown the curveball a total of 57 times. A usage rate of only 9.3%. Despite the low usage rate, it’s still been effective. The .182 batting average and .273 slugging against are the lowest of any pitch Kirby throws. It’s also the only pitch he hasn’t surrendered a home run on.

While the low speed (79 MPH average) has its advantages thanks to the impressive fastball, it’s actually the break that’s made the pitch so effective. Generating 2175 RPM worth of spin on average, Kirby is getting a crazy 57 inches of vertical and 11.8 inches of horizontal break. Even though he struggles with his active spin on the slider, he does not have that same issue with the curve. Kirby’s 92% active spin rate is attributing to an impressive 20.6 inches of the total movement.

The Total Package:

Up to this point, George Kirby looks every bit the number 2-3 starter with potential ace upside. To already have this level of command is impressive. Usually a guy will have the stuff, but the command just won’t be there. Matt Brash is the prime example of that. Kirby seems to be working in reverse order. He’s got the command and his “stuff” is coming along with every start.

Probably the most impressive example of just how good Kirby has been is this…there have been 46 times so far this season where Kirby has had a hitter in a 3 ball count. In those 46 instances, he’s given up only two hits, five walks and has 15 strikeouts. Even when he gets as far behind as possible, Kirby still refuses to let people on base.

Normally I’m big on statcast charts for players but I think Kirby is one I can make an exception for. With only seven career starts, his second and third career starts really messed much of that up. In his four starts since, his average exit velocity against has dropped to 89.5 MPH, hard hit rate has dropped to 36.9% and his K/BB rate jumped to 12.

We are witnessing the future of the Mariners rotation, and damn is it fun to watch.

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