Jakob Junis Joins the Brewers as a Starter

On Monday night, just four days after the Brewers traded perennial Cy Young candidate Corbin Burnes to the Orioles for a package of promising young players and a competitive balance draft pick, Milwaukee signed a pitcher with an even better FIP to take his spot at the front of their rotation.

Sorry, that was misleading. Let’s try this again: After spending five years in Kansas City and two years in San Francisco, right-handed pitcher Jakob Junis has agreed to a one-year, $7 million deal with the Milwaukee Brewers. Kiley McDaniel reported the signing, which according to Ken Rosenthal includes a $4 million salary in 2024 along with a $3 million buyout on a mutual option for the 2025 season. While the Giants moved Junis to the bullpen in 2023, the 31-year-old is expected to join Milwaukee’s starting rotation. After the team non-tendered the injured Brandon Woodruff and traded Burnes, the rotation was looking particularly threadbare, relying on Freddy Peralta and a series of other pitchers with question marks surrounding their health, stuff, age, or some combination of the three.

Peralta, who was worth 3.0 WAR over 30 starts and 165.2 innings in 2023, had excellent stretches last season, including taking home NL Pitcher of the Month honors in August. Still, his 3.86 ERA, 3.85 FIP, and 1.41 HR/9 were all the worst marks he’d put up since the shortened 2020 season. Wade Miley, back on a one-year deal, has been fantastic over the last three seasons, but the Brewers will need him to continue his contact suppression sorcery at age 37. Colin Rea put up 0.8 WAR in 2023; the Brewers are hoping he can post back-to-back seasons with a sub-5.00 ERA for the first time since 2015 and 2016. DL Hall, who came over in the Burnes trade, is a truly exciting young pitcher, but he’s also dealt with injuries over the last two years and ended up in Baltimore’s bullpen in 2023. After a shoulder injury, Aaron Ashby pitched just seven minor league innings last year, while Joe Ross, coming off his second Tommy John surgery, threw 14 minor league innings and hasn’t pitched in the majors since 2021.

Then there’s Junis, who made 40 appearances last season, of which just four came as a starter. He never went more than four innings, despite the fact that he eclipsed that mark in 19 of his 23 appearances in 2022. Working primarily out of the bullpen for the first time in his seven-year career, Junis posted a career-best 4.57 strikeout to walk ratio. His 3.87 ERA was also a career best, and while his 3.74 FIP narrowly trailed the 3.65 he put up in 2022, it did edge out the 3.81 FIP of brand-new Baltimore Oriole Corbin Burnes.

Junis averaged 93.2 mph on his sinker as a starter and 93.7 mph as a reliever in 2023. While we should probably expect him to be closer to the lower mark as a starter this season, it’s still a step up from 2022, when his sinker averaged 91.9 mph. But the sinker isn’t really the story here. Sometimes a pitch percentage chart is all you need — take a look at that yellow line:

In 2022, Kyle Kishimoto wrote his first FanGraphs article about how Junis was on his way to becoming the second starting pitcher ever to throw an individual breaking pitch the majority of the time. In fact, Junis completely remade his arsenal that season. He retired his four-seamer and cutter, increased his changeup usage, and brought back the sinker that had been slowly fading from his mix. Still, the slider is the headliner. Junis threw his slider 50.5% of the time in 2022, and with the return to the bullpen, he increased that rate to 62.5% in 2023. No one else who threw at least 1,000 total pitches used any individual breaking pitch as much as 59% of the time. Stuff+ gives the slider a 129 mark, which ranks 44th among pitchers who threw at least 40 innings in 2023. Its ranked even higher according to Pitching Bot, with a score of 63, good for 30th among the same cohort.

Maybe we should expect Junis to dial back his slider usage a bit as a starter in Milwaukee; perhaps he’ll look to establish the fastball and save his good stuff for longer outings. He won’t be able to dodge as many lefties as a starter. Unfortunately, Junis’ other offerings rank well below average. Stuff+ puts both his sinker and his changeup at 85, while Pitching Bot gives the sinker a 47 and the changeup a 52. Lefties put up an eye-watering .531 wOBA against his sinker, compared to a better (but still not exactly ideal) .398 xwOBA. On the other hand, after running a .339 wOBA against Junis’ slider in 2022, left-handed batters had a wOBA of just .261 against it in 2023, even worse than the .275 that righties put up. Besides, maybe the time for that kind of starting pitching is gone entirely. Maybe the Brewers won’t expect him to pitch into the fifth inning anyway and will let him find out just how many sliders a starting pitcher can throw before he starts spinning himself into the ground like the Tasmanian Devil.

It’s nothing new for the Brewers to bet on their ability to help a pitcher locate the best version of himself, but the rotation is wanting when compared to the Burnes/Woodruff/Peralta triumvirate that fronted it in previous years. You can understand why the team is willing to take a risk on Junis. Maybe the Brewers think they can help him figure out either his four-seamer or his sinker, or unlock some variation on a changeup that works better for him. Or maybe they just need the innings. If he simply reverts back to the 2022 version of himself that the Giants unlocked, well, that version ran a 4.42 ERA and a 3.65 FIP, accruing 1.3 WAR by sandwiching 112 innings and 23 starts around a July hamstring strain. That’s not a terrible baseline, even if the Milwaukee magic doesn’t turn Junis into an frontline starter.