Cardinals Closer Riley O'Brien Emerging as Elite Reliever

The 31-year-old has been dominant to start the 2026 season, providing a bright spot for St. Louis' bullpen.

Apr. 16, 2026 at 12:05pm

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A fragmented, geometric painting depicting the motion of a baseball pitcher, with sharp planes of color and form representing the power and precision of the pitcher's delivery.A cubist interpretation of Cardinals closer Riley O'Brien's dominant start to the 2026 season.St. Louis Today

Despite the St. Louis Cardinals' bullpen struggling overall this season, one reliever has emerged as a standout performer - Riley O'Brien. The 31-year-old right-hander has yet to allow an earned run through 10 appearances, posting a 0.00 ERA and 11-to-0 strikeout-to-walk ratio. O'Brien's advanced metrics back up his strong start, as he ranks in the 90th percentile or higher in several key categories like expected ERA, fastball velocity, and groundball rate.

Why it matters

O'Brien's breakout season comes at a crucial time for the Cardinals, who are in a reset period but currently sit at 10-8 on the year. If he can maintain this level of dominance, it would provide a major boost to the team's bullpen and potentially solidify the closer role for years to come, as O'Brien is under team control through the 2030 season.

The details

After making only 10 total MLB appearances between 2021-2024, O'Brien emerged as a reliable late-inning option for the Cardinals last season, posting a 2.06 ERA in 42 games. He's built on that success in 2026, already recording 5 saves while continuing to miss bats and limit free passes. O'Brien's elite peripherals, including a 99th percentile expected ERA and 100th percentile groundball rate, suggest his hot start is sustainable.

  • O'Brien made 10 total MLB appearances between the 2021 and 2024 seasons.
  • In 2025, O'Brien had a breakout year with the Cardinals, logging a 2.06 ERA in 42 games.
  • So far in 2026, O'Brien has made 10 appearances and has yet to allow an earned run.

The players

Riley O'Brien

A 31-year-old right-handed relief pitcher for the St. Louis Cardinals who has emerged as one of the top closers in the National League to start the 2026 season.

Mason Miller

A relief pitcher for the San Diego Padres who is also off to an insanely hot start in 2026, overshadowing O'Brien's dominance.

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What they’re saying

“If Mason Miller of the San Diego Padres wasn't on the insane heater that he's on, O'Brien certainly would be talked about around the league in general more this season.”

— Patrick McAvoy, Author

What’s next

If O'Brien can maintain his strong performance, he could cement his status as the Cardinals' closer for the foreseeable future. The team will need to monitor his workload and health to ensure he can sustain this level of dominance throughout the season.

The takeaway

Riley O'Brien's breakout start to the 2026 season has provided a much-needed boost to the Cardinals' bullpen, which has struggled overall. If O'Brien can keep up his elite production, he could solidify the closer role in St. Louis for years to come, giving the team stability in a key late-inning spot as they look to return to contention.