How can SF Giants pitcher Jakob Junis get better in 2023?

Jakob Junis has been a great addition to the SF Giants pitching staff this season. But will he be able to build off his success in 2023?

Jakob Junis emerged as the latest successful pitcher to have a resurgent season with the SF Giants. Junis had spent his entire professional career in the Kansas City Royals organization but agreed to a one-year, $1.75 million contract with the Giants before this season and emerged as an excellent swingman for manager Gabe Kapler.

Junis is under team control via arbitration through next season. As the Giants head into the offseason, president of baseball operations Farhan Zaidi has to be wondering what the team can expect from Junis in 2023.

The Giants optioned Junis to Triple-A Sacramento on Sunday after he made his final appearance on the season earlier in the week. He finished the season with a 4.42 ERA across 23 appearances (17 starts). In 112 innings pitched, Junis racked up 98 strikeouts while allowing just 25 walks.

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While his overall numbers were not exceptional, every ERA estimator believed Junis' performance was better than his numbers reflected. He finished the year with a 4.12 xERA, 3.65 FIP, and a 3.65 xFIP.

The Royals originally drafted Junis in the 29th round of the 2011 MLB draft out of high school. Junis slowly worked his way up the organization's minor-league ranks before making his big-league debut with the team in 2017.

From 2017-2018, Junis looked like a promising mid-rotation arm for Kansas City. He posted a 4.35 ERA with 244 strikeouts in 275.1 innings across 50 appearances (46 starts). However, over the next three years, Junis maintained comparable strikeout, home run, and walk rates but recorded an ERA of 5.24 or worse each season. 

The Giants believed there was an easy way for Junis to take a big step forward. Since heading to San Francisco, Junis has stopped using his four-seam fastball and relied more heavily on his sinker and slider.

With the exception of the pandemic-shortened 2020 season, Junis had never thrown his slider on more than 39.9% of his pitches in a season with the Royals, even though it was consistently his most effective pitch. This year, he threw his slider 50.4% of the time.

In 2022, Junis used his sinker at the highest rate of his career since his rookie season. Furthermore, he only threw nine four-seam fastballs all season long. Before this season, he had never thrown his four-seam heater less than 21% of the time.

So were these changes enough for Junis to replicate his success beyond this season? Well, there's an optimistic and skeptical case to be made.

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SF Giants RHP Jakob Junis' strength: His slider

The Giants have been one of the most prominent teams in the broader leaguewide trend of the disappearing fastball. Junis' slider had induced at least a 35.7% whiff rate in every season (except for the pandemic-shortened 2020 campaign) prior to 2022. Opposing hitters only hit .190 against the pitch last season and managed a meager .286 slugging.

With a pitch that good, it's easy to see why the Giants told Junis to throw it more. However, as a pitcher relies more on a single pitch, hitters are more likely to know it's coming and are better prepared to do damage against it. So, Junis' slider was not as dominant this season.

Less dominant does not mean ineffective, though. Opponents swung and missed on 25.1% of their swings against Junis' slider this season and recorded a 28.8% strikeout rate. They hit just .226 with a .381 slugging percentage against his slider. Those numbers are far from elite but considering how often he threw his slider this season, it shows how effective it is.

SF Giants RHP Jakob Junis' weakness: Everything else

The problem facing Junis heading into next season is his lack of a second effective pitch. Opposing hitters hit .315 against his sinker with a .477 slugging percentage this year. His four-seam fastball was hit even harder when he relied on it more from 2019-2021.

If the Giants are going to rely on Junis for more 4-6 inning outings in the future, his slider has not been dominant enough to carry him the second and third time through an opponent's lineup. Perhaps a move to abbreviated 1-3 inning outings could enable Junis to reach another level. A bump in velocity could make his sinker more effective, and opponents would also have fewer opportunities to get used to his slider.

One of Junis' pitches flashed the ability to be the second above-average offering he needs: his changeup. Junis threw his changeup a career-high 15.9% of the time in 2022, but opposing hitters crushed it. Overall, it induced whiffs on just 18.2% of opponent swings while surrendering five home runs, a .364 average, and a .652 slugging.

Those numbers do not suggest Junis' changeup has a lot of promise. However, Junis flashed potential with the pitch all season long. In his first MLB appearance this season, Junis threw his changeup 34% of the time and recorded an elite 43% called strike + whiff rate (CSW%) over five shutout innings against the Nationals. He would rarely rely on it that much in any of his other outings, but it showed the changeup's potential if he can locate it.

Junis' changeup has nearly a 10 -mph gap between the velocity of his fastball and generates above-average vertical movement. The difference between a bad and above-average changeup can be as simple as command. Junis has never thrown his changeup all that much, probably because he is still developing comfort with the pitch.

Jakob Junis was an excellent addition to the SF Giants pitching depth in 2022. Under team control through next season, the front office now must evaluate what role they envision for Junis beyond this season. At this point in his career, the 30-year-old righty only has one above-average pitch. With that said, if the team is confident he can refine his changeup, Junis could be in a position to be even better in 2023.