O’Brien throws the pitch 58% of the time, and it has become the stabilizing force of his entire arsenal. The sinker first emerged as his dominant offering in 2024, but the 2026 version has taken another step forward. He is throwing it around 98 mph, adding roughly an inch of horizontal movement compared to last season, going from 15.9 inches to 17.2 inches of run, while also killing about an inch of vertical movement.

That shape gives him a power sinker with real east-west action, and his ability to consistently fill up the zone with it has been the key to his strike-throwing resurgence.

Everything else plays off that foundation.

O’Brien pairs the sinker with a sharp sweeper at roughly 83 mph that gets around 17 inches of glove-side movement. When layered against the sinker, the two pitches create roughly 34 inches of horizontal separation, giving hitters two pitches moving in completely different directions from similar release points. That is a nightmare look, especially when O’Brien is ahead in counts and forcing hitters to protect against 98 mph arm-side run.

He rounds out the arsenal with a tight bullet slider around 91 mph. The pitch gives him another hard, short-breaking option that tunnels well off the sinker without moving as dramatically as the sweeper. In practice, that gives O’Brien three distinct looks: the power sinker to attack the zone, the sweeper to create chase and horizontal separation, and the harder slider to disrupt timing and keep hitters from sitting on the big two-plane movement.

This is no longer just a nice early-season story, either. O’Brien has been one of the best relievers in baseball through the first month of the season. He ranks third among relievers in fWAR at 0.8, behind only Mason Miller and Louie Varland, and sits tied for second in baseball in saves. For a Cardinals bullpen that needed stability, O’Brien has not merely provided competence. He has provided impact.

The Path Forward for O’Brien

Simply put: Riley O’Brien has pitched like one of the best relievers in baseball. And unlike past flashes, this version is backed by a cleaner arsenal, better strike throwing, and a role that finally appears to fit.

That matters because the Cardinals have been one of the biggest surprises through the first month and change of the 2026 season, and O’Brien’s excellence in leverage has been a major part of that early success.