A quick primer on the sweeper is probably necessary. A sweeper is similar to a traditional slider pitch. The primary difference is that a sweeper has almost double the horizontal movement of a slider while sacrificing some velocity. Shohei Ohtani's sweeper had nearly fifteen inches of horizontal break while his slider had only eight inches of horizontal break last year. His sweeper also ran 2-3 MPH slower than his slider.
Our very own Adam Wainwright broke down the pitch during a broadcast last year. I have also included a video of one of the best sweepers last year that was thrown by Mitch Keller as an example.
Of the various pitchers the Cardinals added this offseason, Sonny Gray, Kyle Gibson, Lance Lynn, and Nick Robertson all use a sweeper. While Lynn's isn't his primary pitch, he did add it this last year. According to run value on Baseball Savant, Sonny Gray's and Kyle Gibson's sweepers ranked first and third, respectively, in effectiveness in 2023 across Major League Baseball. Gray allowed a .097 batting average with a 53.2% K rate on the pitch; Gibson allowed batters to hit .147 against his sweeper with a 40.6% K rate. Sonny Gray's sweeper "swept" nearly fifteen inches horizontally and averaged 84.3 MPH; Gibson's had less break and velocity, but he was excellent at commanding it down and in against lefties and down and away against righties.
Nick Robertson's slider is dubbed as so on Baseball Savant, but its horizontal break (14.6 inches) and its velocity (83.3 MPH) lead me to think that this slider is more than likely an undiagnosed sweeper. Robertson's slider/sweeper was his best pitch last year.
Drew VerHagen had the eighth-best run value on his sweeper last year in baseball, and the Cardinals let him walk this offseason. Justin Lawrence of the Colorado Rockies had the second-best sweeper according to run value. He is rumored to be a trade candidate this offseason. Jordan Hicks also had a dominant sweeper, but he has since signed with the San Francisco Giants.
As an aside, Cardinals' reliever Andre Pallante, in addition to his "death ball", has added a sweeper in hopes of improving his effectiveness against right-handed batters. Hopefully, his sweeper replaces his slider, the worst pitch in his arsenal according to run value by Baseball Savant. Nineteen inches of horizontal break is ridiculous!