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Player Review: Jakob Junis

The Slider Man can!

Arizona Diamondbacks v San Francisco Giants Photo by Thearon W. Henderson/Getty Images

2023 stats: 40 G (4 starts), 86 IP, 3.87 ERA, 3.74 FIP, 10.0 K/9, 2.2 BB/9, 4.57 K/BB, 109 ERA+

Notable: In those 4 GS (7/31, 8/15, 8/20, 8/31): 12.2 IP, 14K, 2 BB 0.574 WHIP, 0 ER (2 unearned)

Jakob Junis’s two (and likely only two) seasons with the San Francisco Giants went almost exactly as the team projected when they signed him. His improvement upon an 89 ERA+ to 109 this season came about because of an adjustment in his usage thanks to the “depth” the team built into the roster. He worked a lot better as a true utility arm.

I guess my favorite stat about Captain Slider, The Sliderman, Jakoby & Slider, etc. is that his 10.0 K/9 ranked 13th in the National League (minimum 80 IP). Better than Zack Wheeler, Zac Gallen, Clayton Kershaw, Corbin Burnes. Sure, that’s diminished by the number of innings, but what a powerful slider it was!

By usage, only three other pitchers in the National League threw their slider more than Jakob Junis, who threw his 868 times. That number accounts for 62.5% of his total pitch usage, a percentage bested by just four other pitchers in MLB in 2023:

Andrew Vasquez, DET (698, 81.8%)
Luke Jackson, SFG (367, 69.9%)
Dauri Moreta, PIT (623, 64.8%)
Jakob Junis, SFG (868, 62.5%)

Using Statcast’s Run Value, his +5 Runs-slider ranked #20 in the NL. Remember back in August when he started against the Rays? 6 of his 7 strikeouts in those 4 innings (plus a walk and 2 hits) came on that slider:

An effective pitch!

Role on the 2023 team

His season really picked up once the calendar flipped from April to May. He ended the first month of the season with a 6.06 ERA/6.26 ERA after 7 appearances (16.1 IP) but posted a 3.36 ERA/3.16 FIP the rest of the way (33 appearances, 69.2 IP).

He only made four starts, though, so you can’t call him a starter, reliever, or combination starter-reliever. He was the Every-Arm? The All-Arm? He managed to do everything the Giants asked him to do but close — which they didn’t need him to do anyway. He was there to be the guy who chewed up some innings without digging a hole for the offense or stabilize a situation to give the lineup a chance later on.

He pitched at least 2 innings in 23 of his appearances and while he was pretty good in most of them, he really was effective in shorter spurts. 25-40 pitches really looked like the sweet spot, so when the slider worked and he could get quick outs he was great.

But having an arm you could throw out there for basically any inning in the game with a decent chance of getting more than that made him extremely valuable to this past season’s Giants team. He was part of one of the best bullpens in the sport for a good chunk of the season. Not only was he the player the Giants hoped he’d be, he was probably so good/effective that he was in the zone of what they projected for Ross Stripling.

Role on the 2024 team

He was the technocratic ideal of a modern major league pitcher. The slider is such a tough pitch to hit and a great slider harder still. He had hamstring issues in 2022 which impacted his slider and a cervical strain at the end of this season that could suggest future problems in his lower half (pitchers don’t get healthier as they age, obviously) — but, he operated nearly at peak performance this past season and gave a lot of teams around the league an idea of how he could help them for a modest sum and at the back of a bullpen.

I don’t anticipate the Giants re-signing him out of free agency and he seems destined for serving a similar utility arm role for another team, but maybe not a second division team. The Rays took Zack Littell — whose arsenal prior to this year vaguely resembled Junis’s — taught him the sweeper and made him a starter. Not difficult to imagine a similar path for Junis, who came into the league as a starter. Even if that doesn’t work out, he’s set himself up for a major league role somewhere.