Brad Keller Is A Cubs Success Story Because of Love (and His Sweeper)

[Jason Ross]

Image courtesy of Rick Scuteri-Imagn Images

There are lots of iconic duos throughout history: peanut butter and jelly, Han Solo and Chewbacca, Batman and Robin. Duos take two items that, on their own, have some flaw, but together, elevate the whole product to something else entirely. Jelly's solo act (a little overly sweet in my opinion) is fine by itself, but when you add in the saltiness of peanut butter, magic happens between those two slices of bread. It creates a salty-sweet combination that neither peanut butter or jelly could dream of without the other. It is within their differences in which fusion is created. 

It is in this same vein, then, that we should begin to examine the 2025 version of Brad Keller. Keller has struggled to find a footing within the confines of a major league role. At times, he's been an acceptable, if unremarkable starting pitcher, but over the last few seasons, had fallen out of favor in Kansas City. Last year, after a trade from the White Sox to the Red Sox, Boston attempted to convert the right-hander to the bullpen; this too looked like a failure. Upon signing with the Cubs, it would have been easy to expect the same to continue. It was here, a duo was born; Brad Keller's sweeper and Brad Keller's slider. 

Brad Keller has always had the slider—it's arguably been his signature pitch, grading out positively with Fangraph's Stuff+ at 102. Despite the quality of the slider, Keller's been searching for a partner to go along the pitch for a while, as nothing else he's thrown has been above the 100 Stuff+ level. Some pitchers can truly be a one-pitch guy, but Keller's slider wasn't that good. It needed something else... it was missing it's peanut butter. 

First, Keller tried to pair his slider with a curveball.. Starting in 2023, he would throw the pitch nearly 20% of the time trying to find that chemistry with his best offering, but it didn't work. His curve was simply a bad pitch, and it graded out poorly in almost any metric you could imagine: Stuff+, movement,  wOBA against, whiff%, etc. The thought process was good; pair the slider with a pitch that would break more vertically, but it was much less than a match made in heaven, The two would break up after just a year. It wasn't meant to be. 

In 2024, the seeds of what he would become were planted. Keller would begin to play around with his slider. First, the slider became a pitch that was less of a horizontal mover, and much more of a vertical-mover, dropping 4 inches relative to other sliders more than it's prior shape. From the ashes of his old slider a sweeper was born, but it was clearly in it's infancy. The pitch was crafted during Keller's stay with the Red Sox Triple-A affiliate after being sent down mid-year, and it would debut at the MLB level at the end of the season. The problem with the pitch was clear when he showed it off in Boston: it was too close to his slider in shape and movement. The two had some promise, but the relationship wasn't love and first sight—these two would need to put in some effort to make this work. 

Below is a movement profile of Keller's pitches last year. Note how close in shape the sweeper (represented in brown-yellow) and the slider (yellow) was. That's a problem, as they were stepping on each others' toes. To truly be a duo akin to the PB&J, they would need to find a way to be themselves just a little more. It's not uncommon in early relationships to try to be too much like your new partner. It was love, but young love. 

It wasn't until this year that the two pitches began to work in harmony, as Keller needed to refine his sweeper further. Now, his sweeper truly does what a sweeper is designed to do: it breaks hard on the horizontal plane. The horizontal movement that he's getting on this pitch now puts him among the league leaders in this category. He combines this with a slider that has some of the most vertical drop of anyone in the league. Most importantly, the velocities of the two pitches are very close, as his sweeper's average velocity is 85.8 mph, and his slider sits at 87.1 mph. These two pitches present very similarly, until one runs away from you, and the other below. Fusion had been achieved. 

It's taken a few years, but at long last, Brad Keller has found a pairing for his signature pitch, and the results show. First, Stuff+ adores the pitch, grading his slider out at a whopping 131, making it one of the best pitches in baseball (for reference, it grades out better than Emmanuel Clase's slider). Baseball Prospectus' Stuffpro and Pitchpro, two other pitch value metrics, also find his pitches elite; particularly loving his sweeper, grading it as one of the best pitches in baseball. And Brad Keller's Baseball Savant page tells the story of his season as well, as he sits near the 90th percentile in expected ERA, expected batting average against, ground-ball rate, hard-hit rate, and chase rate (among others). Don't let the 4.30 ERA on the year fool you—Keller's got the goods.

The improvement Keller has shown goes beyond simply moving to the bullpen. It's a story of refinement, and a story of love; the perfect pairing of two pitches. Brad Keller always had his jelly, his slider. It was a fine pitch, but as a solo act, it was lacking. His slider needed it's version of peanut butter, and he finally seems to have found that in his sweeper. The two work in harmony to be better than they would be alone. They have become a dynamic duo of pitches. Keller's fastball has gained velocity but still grades out poorly on shape models such as Stuff+. Without his sweeper, this may be more of a concern, but as a reliever and with his new offerings, this can be largely forgiven. Isn't love beautiful?

---

What do you think of Brad Keller moving forward? Do you think he can become a high-leverage reliever? Let us know in the comment section below!

View full article