Pirates' Mitch Keller thriving off counterintuitive key to success

Mitch Keller’s path from second-round draft pick to All-Star to ace has been paved with near-constant tweaks to his arsenal. Add a sinker, add a sweeper, abandon the cutter, reintroduce the cutter … the result, according to Statcast, is a seven-pitch mix that has placed Keller among the NL leaders in wins, ERA, innings pitched, and strikeouts.

These adjustments have come with growing pains. Keller’s cutter has been the subject of concern and speculation at various points in his career, and his sinker yielded a .307 batting average when it was introduced in 2022.

Toward the end of last season, Keller had essentially abandoned his curveball, slider, and changeup. His four-seam fastball, cutter, and sinker accounted for 82.4 percent of all of his pitches in the month of September, a month that saw a 5.28 ERA and six home runs in five starts. Those three pitches feature relatively little break and little variance of speed, especially compared to Keller’s breaking offerings.

How did Keller doff the naysayers and find greater success? He did what any pitcher has been taught not to do. He stopped throwing strikes. Or rather, he started strategically throwing balls. While Keller has reduced his rate of outside the zone pitches from 49.8 percent in his first full season (2021) to 47.3 percent thus far in 2024, he has enticed opposing batters into swinging at pitches outside the zone more often, inducing swings on 30.2 percent of such pitches this season compared to 25.5 percent in 2021. In other words, Keller throws fewer pitches outside the zone, but those pitches are more productive.

Pirates' Mitch Keller is thriving outside the strike zone

Keller likes to work down and away from right-handed batters, the natural placement of his cutter, slider, and sweeper, and he now allows the two breaking pitches to venture outside of the zone. The slider and sweeper land outside of the strike zone 54.5 percent of the time. They generate swings 36.5 percent of the time and allow Keller to throw his cutter as a strike more often and more effectively. In 2021, only 42.4 percent of Keller’s cutters were in the zone; now that’s up to 52.2 percent.

Working the cutter alongside his slider and sweeper to righties has been a relatively new strategy for Keller, inspired by working with Yasmani Grandal this offseason. The pitch now limits right-handed batters to a .158 batting average, compared to .271 last season.

Lefties still tee off on Keller’s cutter (.243 average with a .330 wOBA), so there is still room for growth. A more traditional curveball-fastball pairing has been effective against lefties, and the sinker has shown potential in that area as well. Considering Keller’s massive arsenal of pitches, he has the capability to tailor his offerings to each side of the plate, reserving his cutter primarily for righty-righty matchups.

This would be a substantial change for Keller, similar to how he used the cutter early in his career when it was still his most dominant pitch. In 2024, he throws the pitch at a 60/40 split favoring lefties, but before he retooled the cutter after the 2021 season, he leaned 75/25 toward righties. Leaning into the success the pitch has had recently against righties could mean the path to even greater progress runs backwards.