What is Kumar Rocker Doing? Justin Wrobleski & Quinn Priester Overhauls
Kumar Rocker, Justin Wrobleski, Quinn Priester
Rangers Kumar Rocker has ditched his nasty death-ball slider in favor of his cutter and curveball. The catalyst for this is that he struggled against lefties across his first 5 starts of the season (5% K-BB, 5.97 xFIP). Despite the pitch’s ~40% swing-miss, it held an xwOBAcon near .800 in that small sample. Since Rocker’s June 4 return to the Rangers rotation, he hasn’t been throwing this death-ball slider, instead leaning far more heavily on his cutter and lightly mixing in a bigger curveball. His xFIP has fallen back to 3.95 while his K-BB has tripled. He’s made the same basic switch against righties as well—no death-ball slider, way more cutter. Results there are roughly the same as earlier in the year, slightly less swing-miss. 🤠
I think this is a command thing. Particularly against lefties, the death-ball slider and cutter are both located down-in. Looking at heatmaps, the death ball caught more of the plate in April than this cutter has in June (see below). Despite the praise and success his death ball received upon his debut last season, since spring training, something just seems off with the pitch. While I still think that death ball is stellar on shape alone, his results suggest this is a better approach for the time being.
Dodgers Justin Wrobleski made some dramatic changes compared to 2024. He’s averaged ~96.5 mph in June, up over 1 mph from last season. The root of this velocity jump likely ties back to a 4° drop in his arm angle, pulling his release height down from 5.7’ to 5.5’. His extension is up ~2”, suggesting this could be connected to a tweak earlier in his kinetic chain, as most mechanical adjustments are. He threw a slider, curveball, and sweeper last year. This year, he’s turfed the sweeper, and is throwing both a 92-mph cutter and an 88-mph bullet slider that grades out as his best pitch (123 per FanGraphs Stuff+). He’s pulled back on his four-seam usage, is throwing 18% sinker to righties in June, and his changeup has ~9” less vertical break (dropping more) sitting 2 mph hotter than it did last year (likely a kick-changeup). 🎬
The net result of all this is that Wrobleski posted a 23% K-BB and a 3.11 xFIP against righties in June, a jump from his combined 2024 MiLB/MLB performance versus righties, which was a 17% K-BB and 3.92 xFIP. Wrobleski also sat in zone 61% against righties in June (above average) and still maintained a 12% swinging-strike rate (average). For all the crap the Dodgers get for blowing out arms, this overhaul feels under the radar. I have no idea what his role is when other arms get healthy, but he’s an MLB starter of some kind. It feels like he’s auditioning to be a trade piece for another team come deadline.
Brewers Quinn Priester quietly posted a 2.76 xFIP / 22% K-BB in June, both notable improvements from May. His cutter usage has increased from 14% in May to 31% in June against lefties and from 3% to 17% against righties. It’s a relatively average shape, sitting 91 mph with 12” vertical break and 1” glove-side movement, more lift than the average cutter for that velocity band. The most notable thing is that FanGraphs Location+ has his cutter at a 120 since his May 24th outing, plus-plus location of the pitch. This is validated by the 54% ground-ball rate, 12% swinging-strike rate, ~.300 xwOBAcon combo, which suggests all-around success of the pitch. 🍺
The most interesting thing is that the cutter is not purely a behind-in-count pitch that he’s using to help the performance of his sinker and slider in early count spots. He’s using it most in the first or second pitch of an at-bat. When the Brewers acquired Priester from the Red Sox, I didn’t think much of it. The Red Sox were the team that pushed him into cutter usage, but the Brewers have taken it to another level. There’s very little strikeout upside here, but he’s limiting contact quality enough to become interesting. 3.50-3.75 ERA rest of season feels attainable.
The Brewers are one of 7 teams with a barrel rate under 8% allowed by their starting pitchers. They also lead MLB in cutter usage. These two facts are related.
