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The best reliever in baseball so far this year, according to Fangraphs WAR, has been the Padres’ Mason Miller -- a fact that will surprise no one. The second-best has been the Blue Jays’ Louis Varland, who has followed up the 15 postseason appearances he made last year by starting this season with 13 scoreless innings. But the third-best -- a pitcher who also hasn’t allowed an earned run this year -- is the Cardinals’ Riley O'Brien.
O’Brien has been brilliant from the start for St. Louis this year, striking out 15 batters, issuing zero walks and giving up only six hits in 13 1/3 innings. Any Cardinals fan can tell you, too, that these have been high-stress opportunities for O’Brien. The Cardinals’ bullpen has a 5.17 ERA (and that’s counting O’Brien) and a 5.3 BB/9 rate. There are already five games this season in which a St. Louis reliever has walked three or more batters in an inning. That’s a lot of fires for O’Brien to keep putting out. You could make an argument that the Cardinals (14-10) would not having a winning record without him.
The key to O’Brien’s success has been his ability to get strikeouts while still having his sinker work to keep the ball on the ground; as FanGraphs’ Ben Clemens put it, O'Brien has gone full Zack Britton. O’Brien has established himself as the Cardinals’ closer, already racking up seven saves -- one more than he did all of last year. Along with lefty JoJo Romero, O'Brien has been one of the few reliable arms in a bullpen that is barely hanging on, for a team that is spending this season mostly figuring out which pieces are going to be a part of this organization for the long term.
You would think this sort of dominance would secure O’Brien’s status as one of those pieces, alongside other players off to strong starts such as Jordan Walker, Masyn Winn and JJ Wetherholt -- three obvious building blocks moving forward. But while the Cardinals wouldn’t part with any of those three if you offered them Shohei Ohtani -- OK, maybe if you offered Ohtani -- O’Brien sure looks like someone who, if he keeps this up, is going to be prime Trade Deadline material come July.
It would be silly not to trade him. The reason for this, of course, is his age. Even though O’Brien has pitched only 71 2/3 innings in his career --one fewer inning than 23-year-old Reds righty Chase Burns -- he is a downright grey-bearded 31 years old. He is in fact the third-oldest Cardinal, behind fellow reliever Ryne Stanek and utility infielder Ramón Urías, both of whom are signed to one-year contracts.
O’Brien’s career arc has been so unconventional that he hasn’t even reached arbitration yet. He was waived by both the Reds and the Mariners, who eventually traded him to the Cardinals for cash considerations, and in his first season in St. Louis, 2024, he had an 11.25 ERA in eight mop-up appearances. In other words: It took him quite a while to find his way.
The Cardinals have O’Brien under team control through the 2030 season, and that might sound like it would be within the team’s current competitive timeline. (If the Cardinals aren’t competing in the NL Central by 2030, something has gone terribly wrong.) But by then, O’Brien will be 34 years old, and who knows what will have changed in his career, and in the Cardinals system. Four years ago, O’Brien had a 7.12 ERA at Triple-A Tacoma; No matter how good his sinker might be right now, are you sure you want to count on him being this pitcher in four years? Life happens fast for relief pitchers.
The entire structure of the Cardinals’ rebuild is based around bringing in as much young pitching as possible. If there aren’t pitchers coming up in the system over the next four years who can displace a guy in his mid-30s, the entire structure of the rebuild will have failed.
While this team’s early success has been nice to see, the main point of the 2026 season is to find young pieces to build around for the future and then flip players who aren’t part of that for players who will be. When you look at Cardinals who have shined in the first month of the season, they are players like Walker, Winn, Wetherholt and (to a lesser extent) Alec Burleson, players who are still young and -- if the coaching staff does what it is here to do -- likely to keep improving. And then there is O’Brien, who is only nine years younger than his manager, playing a position (reliever) that is famously impossible to count on in the long term, or even the short term.
There is nothing contending teams need at the Deadline more than relief pitching. The Padres are not trading Miller this year, and the Blue Jays are not trading Varland. Even with this start, the Cardinals are almost certain to be sellers this summer. And they will have no better trade piece than O’Brien who, in addition to potentially being the best reliever on the market, will offer four more years of club control, only adding further to his value.
The A’s got Leo De Vries (MLB Pipeline’s No. 4 overall prospect) for Miller at last year’s Deadline. There is no way the Cardinals get that sort of return for O’Brien, no matter what he does over the next few months. But if the Cardinals can get any sort of significant prospect haul back for O’Brien -- a player they essentially got for free -- they would be foolish to turn it down. And this front office has shown itself to be anything but foolish so far.
O’Brien has been a joy to watch as a Cardinal this year -- one should appreciate it while one can.