What’s the next step for Mariners’ George Kirby after big rookie season?

The Mariners had a successful season in 2022, and a big part of that success was the play of young players.

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It starts, of course, with superstar outfielder Julio Rodriguez, who should win AL Rookie of the Year and get some MVP votes.

There was also second-year catcher Cal Raleigh, a Gold Glove and Silver Slugger finalist who led all MLB catchers in home runs.

Logan Gilbert pitched well and was among baseball’s best and most valuable pitchers in his second big league season.

While Matt Brash struggled as a starter, he emerged as a very dangerous bullpen arm for Seattle’s playoff run. And sticking with the bullpen, who saw Penn Murfee having the season he had?

But those weren’t the only youngsters to become key members of the Mariners in 2022, as rookie right-hander George Kirby was stellar after entering the rotation in May. In many seasons, Kirby may have won Rookie of the Year.

In 25 starts, Kirby posted a 3.39 ERA across 130 innings with 133 strikeouts to 22 walks while winning eight starts. He gave up 12 home runs in 2022, but all of those came in his first 10 starts. Kirby didn’t surrender a long ball after July 27.

And that was just the regular season.

Kirby saved his best for last, pitching eight scoreless innings in two playoff appearances. He earned the save with a scoreless ninth inning in Game 2 of the Wild Card round to cap off the Mariners’ 10-9 comeback win in Toronto in what was his first-ever MLB relief appearance.

George Kirby shuts the door and sends the @Mariners to the ALDS! pic.twitter.com/xw7Z2Z2eQ5

— MLB Pipeline (@MLBPipeline) October 9, 2022

He then tossed seven scoreless innings in an elimination game against the Houston Astros in the ALDS.

Kirby unfortunately hasn’t gotten the love or credit he deserves for the outing against Houston as the game went 18 innings and the M’s lost, ending their season. But it was truly a masterful performance and a great way for Kirby to end his first MLB season.

.@gkirb98 has ice in his veins. pic.twitter.com/wc6VIaV8jU

— Seattle Mariners (@Mariners) October 15, 2022

So yeah, safe to say the 2019 first-round pick had quite the successful rookie campaign, and Kirby has cemented himself as a long-term fixture in the Mariners’ rotation.

So what’s the next step for Kirby to build off his stellar 2022 season? Let’s dive in.

The other numbers

When looking at Kirby’s Statcast page of advanced metrics, it’s easy to see where he excelled and where he struggled as a rookie.

His walk rate was elite, ranking in the 96th percentile. He also had an above-average strikeout rate in the 63rd percentile.

But Kirby left a bit to be desired when it comes to hard contact.

Kirby ranked in the 28th percentile in average exit velocity, 22nd percentile in barrel rate and 44th percentile in hard-hit rate.

Why that’s important is simple: the harder you hit the baseball, the more likely you are to have success at the plate.

Per Luke Arkins of Prospect Insider, MLB hitters hit .488 with a .954 slugging percentage and 5,119 home runs in 2022 on hard-hit balls (95-plus mph exit velocity) compared to just a .219 average and .254 slugging percentage with 55 homers on non-hard-hit balls.

Obviously, pitchers can work around hard hits. Kirby pitched very well despite allowing a lot of loud contact. Robbie Ray won his Cy Young Award in 2021 while ranking poorly in hard contact allowed. It’s also something Gilbert has struggled with in his two MLB seasons.

If Kirby is able to better limit hard contact next season, watch out.

Additionally, Kirby’s strikeout numbers were good, as he posted just over one per inning. What makes that number a bit surprising is that his whiff (swing-and-miss) rate was just 15th percentile in baseball this year. He also had a chase rate (swings at pitches outside of the strike zone) in the 45th percentile.

Kirby is an elite command pitcher, and he threw strikes nearly 70% of the time in 2022.

George Kirby set an MLB record today when he didn’t throw a ball until his 25th pitch. 😱

(MLB x @CueHealth) pic.twitter.com/BhGUJpYLUi

— MLB (@MLB) August 24, 2022

As he gets a better feel for MLB hitting as well as his own arsenal, we should see him be more comfortable expanding the strike zone and potentially getting more swings and misses out of the zone, too.

That brings us to …

The Arsenal

The two biggest reasons Kirby had the success he had in 2022 are one, he throws a lot of strikes as referenced above, and two, he has an elite fastball.

Kirby averaged 95.3 mph on the four-seamer, and it was far and away his most-used offering and his best pitch.

Kirby threw the heater 45.4% of the time, and for good reason. Opponents hit just .221 off it with a .345 slugging percentage. It also yielded the best whiff rate (26.4%) of the six pitches he threw, and his best strikeout rate at 30.4%. It was also an elite pitch in all of baseball with a minus-18 run value, per Statcast, which was the 17th-best pitch in baseball by the metric.

Kirby’s fastball should remain a great pitch for him for a long time, but what about his others?

Kirby’s curveball was his second-most-used pitch at 13.3%, and it wasn’t a great pitch for him, with opponents hitting .305 off it with a .492 slugging percentage. He also didn’t generate many swings and misses (13.7% whiff rate) and had just a 10.8% strikeout rate with it, his lowest rate of any pitch.

Kirby used two other breaking balls in 2022, one a slider and the other a firmer cutter.

The cutter checked in at 12.2% usage rate and 88.3 mph. While the numbers aren’t very good (.362 batting average and .639 slugging percentage), it’s worth noting the expected average and slugging numbers, per Statcast, were much better at .268 and .432. He also got a fair share of swings and misses with the cutter at a 21.5% whiff rate and a 23.3% K rate. He did allow four home runs on the pitch, though.

The slider was a bit slower at 85.5 mph and had more movement, and it had better success than the cutter in terms of numbers against with a .283 average and .370 slugging. The expected numbers on that pitch were also better with a .205 xBA and .251 xSLG. He didn’t get quite as many whiffs (14%) or strikeouts (19.1%) as the cutter, though. The slider was Kirby’s fourth-most used pitch at 8.9%.

Kirby’s changeup (8% usage) also got hit with a .279 average and .395 slugging percentage. It was used far more against lefties than righties, and he got whiffs 15.8% of the time and a 13.6% K rate.

What Kirby did do in-season, though, was add a two-seam fastball/sinker. Much like Ray, who also added the pitch during the season, it was huge for Kirby.

The sinker was used 12.2% of the time and had great movement and was only a tick slower than the four-seamer at 94.7 mph. Opponents hit .266 off it with a .291 slugging, but the expected average was .199 and expected slugging was .268. Kirby didn’t get many swings and misses with the sinker (11.9% whiff rate), but he recorded 25 of his strikeouts (28.1% K rate) with it, using it to backdoor right-handers and starting it inside to lefties before running it back over the plate.

Some nasty paint from George Kirby. 🤢 pic.twitter.com/hV8ECE5ff2

— MLB (@MLB) August 31, 2022

The four-seam and sinker are legit weapons for Kirby, but if he wants to get more chases and swings and misses in 2023, the secondary offerings need to improve.

The cutter was a good pitch in terms of getting strikeouts and whiffs, but it was hit harder than Kirby’s other offerings. The slider, meanwhile, had better numbers but yielded fewer whiffs and Ks. Those two seem to have the most promise of Kirby’s secondaries, and it will be fun seeing how those pitches – as well as the curve and changeup – look next season. With even marginal improvement in the secondary department, Kirby could really take off in Year 2 as an All-Star and a true frontline starter, which is absolutely possible given what we saw this season.

Come this time next year, it’s not out of the realm of possibility that the Mariners will still be playing baseball in the World Series. It’s also not out of the realm of possibility that Kirby not only emerges as one of the team’s two best starting pitchers over Gilbert and Ray, but that he could be the best pitcher on the staff over All-Star Luis Castillo.

Very few pitchers have the command and stuff that Kirby has, and he’s shown a knack for making strong in-season adjustments such as eliminating home runs, implementing the sinker, and coming through in pressure situations.

2022 was a fantastic start to Kirby’s career, and with some improvements to his non-fastball pitches and a reduction in hard contact, he could be talked about as one of the true aces in MLB in the very near future. The tools are all there.

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