What Should The Cardinals Do With Riley O’Brien?

It’s been a weird year for closers. Edwin Díaz, Josh Hader, Ryan Helsley, Emilio Pagán, Carlos Estévez and others are on the injured list. Jeff Hoffman lost his job with the Blue Jays. Pete Fairbanks, just reinstated from the IL, has an earned run average of 10.00. Devin Williams and Andrés Muñoz have ERAs over 5.00. Bryan Abreu, filling in for Hader, has an ERA over 8.00. The Cardinals, meanwhile, are getting great results from a guy who hardly pitched in the majors before his 30th birthday.

St. Louis acquired Riley O’Brien in a very small trade in November of 2023. At the time, O’Brien didn’t even have a 40-man roster spot with the Mariners. All 29 other clubs had passed on claiming him when Seattle placed him on outright waivers in the summer of 2022. He was about to become a minor league free agent, but the Cards saw enough in O’Brien to send cash to Seattle to acquire him and place him on their 40-man roster so he couldn’t hit the open market.

The track record at that time wasn’t much to go on. An eighth-round pick of the Rays in 2017, O’Brien began his career as a starting pitcher. He was flipped to the Reds in August of 2020 for left-hander Cody Reed. Cincinnati added O’Brien to the 40-man roster that November to keep him out of the Rule 5 draft. Things didn’t work out with the Reds. O’Brien made a brief major league debut in 2021 but posted a 4.55 ERA in Triple-A. He was designated for assignment early in 2022 and shipped to the Mariners for cash or a player to be named later.

O’Brien was moved to a relief role in 2022, a switch that didn’t immediately bear fruit. He finished the year with a 7.03 ERA in 39 2/3 Triple-A innings. He seemed to turn a corner in 2023 when he threw 55 Triple-A innings with a 2.29 ERA in the hitter-friendly Pacific Coast League. O’Brien struck out 37.7% of batters faced and induced grounders on 57.1% of balls in play. His 13.6% walk rate showed that he was still working on his control, but the Cards were intrigued enough to make that small trade and dedicate a 40-man spot to him.

That didn’t pay off right away. O’Brien suffered a flexor strain early in 2024 and missed most of the season. He was only able to make eight big league appearances and 14 more in Triple-A. He went into 2025 with only 10 1/3 major league innings under his belt. He turned 30 in February of that year, just before the season started.

O’Brien was finally able to break out in the big leagues last year, as he gave the Cards 48 innings with a 2.06 ERA. He wasn’t really as good as that ERA would suggest, however. His 11.1% walk rate was quite high and his 22.6% strikeout rate only average. His 54.1% ground ball rate was good but he got a lot of help from a .252 batting average on balls in play and 82.8% strand rate. His 3.61 FIP and 3.82 SIERA suggested he was good but not quite as dominant as the ERA made it seem.

The Cardinals sent him to the minors a few times last year and burned his final option year. That situation could push a pitcher off the roster, but that’s not going to happen anytime soon with O’Brien. He has taken over the closer’s role in St. Louis, with a 2.70 ERA and 12 saves in 20 innings so far this year. Though that ERA is higher than last year’s, the numbers under the hood look far better. His 29.5% strikeout rate, 2.6% walk rate and 62% ground ball rate are all huge improvements. His .320 BABIP this year actually skews a bit to the unlucky side. His 2.06 FIP and 1.67 SIERA think he actually deserves far better than his ERA.

The results are backed by a strong arsenal. O’Brien is averaging 98.4 miles per hour with his sinker, a pitch he is throwing 59.2% of the time. This year’s most-used secondary pitch is a sweeper that comes in around 83.8 mph, though he’s also using a 91.5 mph slider, giving hitters two different breaking pitches to watch out for. There’s also a changeup nominally in the mix, though that has made up less than 1% of his offerings this year.

O’Brien’s success is a big reason why the Cardinals are playing a bit above their heads right now. They have a 24-18 record despite an essentially even run differential. They have scored 194 runs and allowed 193. The +1 run differential gives them an expected win-loss of 21-21, but they have gone 8-3 in one-run games and 5-1 in extra innings. In short, they’ve played like a .500 team on the whole but have eked out three extra wins in close contests. O’Brien locking down 12 saves and earning three wins has surely played a role in tipping those scales.

It puts the Cards in an interesting spot this summer. They had planned for this season to be an evaluation year. They traded away Sonny Gray, Willson Contreras, Nolan Arenado and Brendan Donovan in rebuilding moves. The plan was to spend 2026 letting less-established guys accumulate lots of playing time, so the club could figure out who is a building block and who has trade value.

Perhaps the Cardinals will fall back in the standings and make things easier for the team brass. If not, it could lead to some tough decisions. The front office probably doesn’t want to buy at the deadline since that would require subtracting from the farm system, at a time when they are trying to build it. In fact, they probably want to do more selling, with guys like Lars Nootbaar, JoJo Romero, Dustin May, Nolan Gorman and Alec Burleson being some logical trade candidates.

O’Brien will be a very interesting player to track as well. On the one hand, he is not close to free agency. He came into this year with one year and 129 days of service time. He’s under club control for four more seasons after this one. He could qualify for arbitration this offseason as a Super Two guy, but even he does, four arb years for what looks like a potential high-end reliever is a great thing to have. There’s a case for keeping him around.

On the other hand, reliever performance tends to be quite erratic. O’Brien is 31 years old and doesn’t have a long track record of big league success. He walked 11.6% of batters faced in his minor league career. He had a 13.1% walk rate in the majors coming into this season. He’s now walking just 2.6% of opponents this year. Did he suddenly go from poor control to elite, or is this going to regress?

There’s also the ever-present injury concerns with a pitcher, especially one who throws almost 100 mph. Most high-velocity pitchers deal with arm issues these days and O’Brien had that aforementioned flexor strain in 2024.

There are many moving pieces here, making O’Brien an interesting player to watch in the coming months. As mentioned up top, lots of clubs have gotten poor results from their closers. Relievers are always in demand at the deadline and that need will perhaps be even greater this year. There’s an argument for the Cards to cash in while O’Brien is putting up good numbers. When they plan to truly contend in a few years, he’ll be pushing into his mid-3os and who knows what his status will be at that point?

Between now and the August 3 deadline, there are many ways it could tip. O’Brien could keep locking down games but he could also see his control slip or he could perhaps get hurt. The team could keep winning games and hang in the race or they could slip back. Trade talks won’t earnestly ramp up for a while but the Cardinals will have some interesting phone calls this summer.