Arizona Diamondbacks pitcher Merrill Kelly has been working on his slider ahead of this season. In fact, the right-hander has been using this spring training to develop that pitch to add to his repertoire of pitches. New pitching coach Brian Kaplan believes the slider will help make Kelly’s sinker and other pitches more effective.
Merrill Kelly on an area of his game he’s locked in on this spring: pic.twitter.com/L6neCDcvY3
— Alex Weiner (@alexjweiner) February 28, 2025
Merrill Kelly Trying to Develop His Slider in Spring Training
Multiple Pitches
Kelly has never been a hard thrower, but he does bring a multiple pitch selection. In no particular order, he mixes in changeups, curveballs, cutters, four-seam fastballs, and sinkers. All these pitches have shown that he is able to fool hitters when needed. To now mix in a slider gives him six pitches to work with and stymie hitters.
Not Overpowering
Kelly is now developing his slider and will be the first one to tell you that his game is never going to be about overpowering hitters with his fastball. He certainly has earned the designation of “pitcher,” not “thrower.” Kelly also will let you know that he really doesn’t shy away from throwing different pitches in different counts.
Introduced in 2023
Kelly introduced the slider in 2023, using it 6% of the time. Its usage increased to 12% in 2024. In Thursday’s spring game against the Seattle Mariners, he threw eight sliders, generating four swing-and-misses on five swings. His velocity was up as well, averaging 94 MPH on the fastball. He used all six pitches in his arsenal to get outs in and around—a very strong outing.
Merrill Kelly has always been an effective arm, but new Diamondbacks pitching coach Brian Kaplan might have helped unlock a new weapon for the righty.@shoewizard59 spoke to Kelly about the development and usage of a somewhat unfamiliar pitch.https://t.co/AweFUfeVSw
— Alex D’Agostino (@AlexDagAZ) March 7, 2025
An Injury-Filled 2024 Season
Kelly had two very strong seasons, 2022 and 2023, going a combined 25-16 with a 3.33 ERA. He was the workhorse of the Diamondbacks’ pitching staff. But 2024 was a shorter season for him. He ended up with a shoulder injury in late April. That injury kept him out four months before an August return. Kelly also dealt with cramping issues. However, he worked with doctors during the offseason to adjust his approach and hopefully alleviate the issues.
Last Year of Kelly’s Contract
Kelly is now 36 years of age and in the last year of his contract. He has mentioned he would like to finish his career in Arizona, where he grew up. A product of Desert Mountain High School in Scottsdale, then Yavapai Community College in Prescott, and a graduate of Arizona State University, he lives in Arizona year-round. It would be hard to visualize him on another team so close to the end of his career.
When Healthy
This spring, Merrill Kelly is continuously improving his slider and his approach. There is no doubt that he is a force on the mound when he is healthy. If he can recapture his 2022-23 peak performance, the Diamondbacks will have three potential aces at the top of their rotation. Having Kelly along with Corbin Burnes and Zac Gallen leading the pitching staff can only give the team an edge over their competitors, and a National League postseason spot could be theirs.
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