The Unlikely Duo Dominating in the Cardinals Bullpen

The St. Louis Cardinals bullpen has been dealing lately. Of course, guys like closer Ryan Helsley and offseason acquisition Phil Maton are getting the job done, but starter-turned-reliever Steven Matz and Kyle Leahy, in his first full year in the majors, have been two of the best arms out of the ‘pen. 

The bullpen as a whole has been solid for most of the year, but especially over the past month. Since April 27, Cardinals relievers have a 2.81 ERA, the third lowest in MLB.

Leahy totaled just 50 innings between the 2023 and 2024 seasons. So far this year, he has 29.1 innings pitched. The 27-year-old is finally getting his first full season in the big leagues and has not disappointed. He has an ERA of 2.15 and a WHIP of 0.82. 

Most importantly, manager Oliver Marmol and pitching coach Dusty Blake trust him in big spots. Leahy has appeared in mostly medium or high-leverage situations. He has made most of his appearances in the seventh and eighth innings. 

Matz is at a completely different point in his career. He signed with the Cardinals back in 2022 on a four-year deal, and up to this point, the results have not always been good. However, he has taken to his new role as a lefty in the ‘pen very strongly. Left-handers are slashing .171/.209/.244 against him in 2025. 

Overall, in 31.2 innings, he has a 1.99 ERA and a 1.81 FIP. He has primarily acted as a low-to-medium-leverage reliever. He has faced batters in every inning from the first to extras, though he has seen more work in other sixth and seventh than any other innings.

This season, Leahy has significantly decreased the usage of his fastball. Last year, he threw a four-seamer about 44% of the time. That number has dropped to 30.8% this year. He has also introduced a sinker this year and increased his curveball and changeup usage.

He sits in the 94th percentile for pitching run value and the 100th for breaking ball run value. His wOBA against is in the top four percent of pitchers in MLB. 

The righty has slightly increased his groundball rate and decreased his fly ball rate this year, increasing his groundball-to-fly ball ratio from 0.97 to 1.24. With the Cardinals’ solid defense, Leahy can afford to stick to his game and pitch to contact. 

After an injury-plagued 2024 season, Matz looks like a new person on the mound. His walk rate is a minuscule 2.4%, his xERA is a low 2.73, and his fastball run value is in the 94th percentile. 

Like Leahy, Matz does not rely on getting strikeouts, swings, or misses. He gets a lot of outs in the air and limits barrels. 

The sinker has been his primary pitch this year, and he has essentially eliminated the slider from his arsenal. His changeup remains his secondary pitch, though he is using it less often in favor of his curve. Opponents have not hit well against his curve all year long. Batters are slugging .130 against it.

Last year, JoJo Romero and Heslely were the most dominant pitchers out of the Cardinals bullpen. Helsley is still the guy, but Romero has taken a step back this year. While Romero remains the go-to lefty in high-leverage situations, Matz has been fantastic in his new role. Meanwhile, Leahy has provided much-needed support in dangerous situations and looks like he could be the seventh-inning setup man long term.