While Mitch Keller's sinker is the big focus for most when looking at his breakout, another major adjustment isn't talked about nearly enough, despite having an equal, if not greater impact
2022 was a big make-or-break season for Pittsburgh Pirates’ right-hander Mitch Keller. Going into his age-26 season, Keller had yet to fully put it all together. At times he flashed the talent that made him one of the best pitching prospects in baseball, but nothing seemed to click for the youngster. That was until this year when Keller finally seemed to find his groove.
Most contribute Keller’s success to his newly minted sinker, and that’s one major reason for his success. On May 25th, Keller used his new pitch a third of the time. It was only the second game he had ever thrown the pitch, but from that point forward, he significantly incorporated it into his arsenal.
In total, he pitched 123.2 innings from May 25 through the final game of the year. He worked to a 3.20 ERA, 3.67 FIP, and 1.35 WHIP. Keller became much more of a ground ball focused pitcher. He had just a 20.5% strikeout rate but a decent 8.8% walk rate and an outstanding 49.4% ground ball rate. Opponents managed an 88.2 MPH exit velocity against him, which is slightly above the league average. His combined ability to induce grounders and limit super-hard contact led to an HR/9 of just 0.65.
His sinker undoubtedly played a major role in his breakout campaign. With a -7 run value, Keller’s sinker-ball was the 27th most valuable of its kind in baseball last year. On a pitch-by-pitch basis, his sinker was better than Alek Manoah’s sinker, a guy who was highly praised for his sinker as a prospect and was a Cy Young finalist this year. However, another major factor that Keller worked on was his slider, and that was the second large reason Keller was so well last year.
Keller made major improvements to his slider. In his first seven starts of the year, Keller’s slider topped out at seven inches of horizontal break and bottomed out at two inches of break. Then for his next five starts, he saw a slight uptick, now sitting at 7-10 inches of horizontal movement. At the time, these were career-best numbers for Keller.
Then on June 16th, Keller made a major discovery with his slider. He hit 16 inches of horizontal break, the most he had ever averaged in a single game with this offering by a half of a foot. From that point forward, Keller never dipped below 15 inches of horizontal break with his slider. His previous high was just ten inches.
Not only did he add significant horizontal break, he also added vertical break. From 2019-2021, Keller typically sat around 30-40 inches of vertical movement. That’s still above average, but then after making significant adjustments, Keller hit 45 inches on June 16, a career-best mark. He never dipped below 41 inches after that and topped out at 46 inches.
Baseball YouTuber Jolly Olive recently posted a video about Keller’s breakout, which you can watch here (I highly suggest any Pirate fan to watch this video about Keller as it goes more into detail with his breakout). However, while this video covers many aspects of Keller’s breakout, it didn’t specify just how much Keller improved his slider last year. Keller’s slider went from averaging 3-5 inches of horizontal break, then all of a sudden going to 15-20 inches on average.
Everyone talks about Keller’s new sinker. It’s very much a reason he did so well last year. But his improved slider is another massive reason Keller was great during the 2022 season. Keller had an above-average whiff rate with both his slider and fastball, and he did have a below-average strikeout rate during his breakout. If Keller continues to work on improving, we could see him take another step forward in 2023.