John Schreiber is working on a brand new pitch this offseason

Red Sox

“Oh, that’s it.”

John Schreiber’s brand new pitch could make the Red Sox’ bullpen even deadlier than it was last year. Barry Chin/Globe Staff

One of the Red Sox’ deadliest pitchers could be even more lethal by next season.

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Reliever John Schreiber appears to be adding a cutter to his arsenal. A video posted to the Driveline Baseball account on X shows Schreiber working on this cutter with former MLB pitcher Brandon Mann.

In this video, Schreiber details how he grips the baseball when he throws his new cutter, which he throws for the first time in the video at “slider speed.” After Mann tells him to “think more fastball,” Schreiber threw another cutter at 87 miles per hour, which was nearly eight more mph than the velocity of his first pitch.

“Oh, that’s it,” Mann said after Schreiber threw his second pitch.

If Schreiber can master the cutter before Opening Day, it will be the fifth pitch he has in his arsenal. Last season, he relied on four pitches: a slider, a changeup, a four-seam fastball, and a changeup, although he only used his changeup 8.3 percent of the time, according to Baseball Savant.

He won’t be the only Red Sox pitcher with a cutter next season. Tanner Houck, Brayan Bello, Josh Winckowski, Nick Pivetta, Chris Martin, Kutter Crawford and most notably Kenley Jansen all threw cutters at the major-league level, but only Martin, Crawford and Jansen used it more than 20 percent of the time.

Schreiber had an up-and-down 2023 after his breakout 2022, posting a 3.86 ERA in 46.2 innings pitched. If his new cutter becomes a legitimate weapon, that number will almost certainly go down.

The Red Sox’ bullpen, assuming everyone stays healthy, looks to continue its dominance in 2024. If Schreiber’s cutter develops well, that bullpen will only become better.