After a big trade for Sonny Gray, the next NL Central righty the Red Sox have added might seem considerably less interesting, given that new addition Johan Oviedo has spent most of five seasons for St. Louis and Pittsburgh being decidedly unremarkable. You wouldn’t look at a career 4.24 ERA and a 4.61 FIP -- to say nothing of a 15-26 record -- and find much to be excited about.
That may be true, and yet we also have learned endlessly that teams aren’t just looking at ERA or win/loss record to try to find value; this is why Dylan Cease got valued, and so did Devin Williams, and really so did Gray, all despite ERAs in the 4s last year. It’s because ERA isn’t a terribly predictive metric, not more so than some of the fancier advanced models, and even not more so than something as simple as looking at strikeouts and walks.
Even so, a trade for the coming years isn’t really about what a player’s career to date has looked like, because things can and do change. It’s about what a player looks like now, and what a team thinks that he can be going for them going forward. In Boston’s case, it’s about Oviedo’s fastball, and the very different way it behaved last summer after he recovered from the Tommy John surgery that cost him all of 2024.
Go back to 2023 for a moment, when Oviedo ate 177 decent-enough innings for Pittsburgh. That year, he did so with a very good slider (+11 Run Value, a top-dozen mark) and a brutally poor fastball (-12 Run Value, a bottom-20 mark). It was so noticeable an issue that Davy Andrews, writing at FanGraphs that year, started a look at Oviedo with these prescient words: “Johan Oviedo has a fastball problem.”
That was a problem in the most modern way, because while he threw it hard, averaging nearly 96 mph, he also had exceedingly poor vertical movement on it, among the worst in baseball, lacking anything resembling “rise.” Major League hitters can time that up, and they clearly did. He had a fastball problem.
Oviedo missed the entire next year with the elbow surgery, and spent the first half of 2025 rehabbing his way back through the Minor Leagues. When he resurfaced in August, the fastball suddenly looked very different, adding five inches of rise, which got it quite close to at least being average in that regard. The results were noticeable: In 2023, that pitch allowed a .273/.465 BA/SLG, yet in 2025, it was .149/.383. Whiff rate? A jump from 19% to 31%.
It’s not, to be clear, suddenly a Skubal-level heater. But that’s a big change, and it’s reflected in the Stuff+ metrics (evaluates the quality of a pitch’s velocity, movement and quality) which had graded it as well below-average (82) in 2023 and a pretty solid pitch (115) in 2025 -- actually a lot closer to the top of the leaderboard than you’d think. It stopped being something like a bad sinker, and started being something like a usable four-seamer.
It’s not fully clear how he did that, though it’s likely to be about a change in grip, and either way, some credit should go to the Pittsburgh pitching development system there. It didn’t, obviously, suddenly make him a star; there’s no amount of fastball shape improvement that will make a 14% walk rate OK, and that might limit what he’s really able to do with it. The story here is not “ace in the making,” so much as “a really, really interesting change that’s worth highlighting.”
The Red Sox, contrary to popular belief, don’t prevent their pitchers from throwing fastballs. They just try to not let them throw bad fastballs for the sake of saying you did. The old version of Oviedo very much had “a bad fastball.” The new version? Just might be considerably more interesting than you’d think, and it’s not that hard to see what Boston saw in him. It’s not, to be clear, the ERA.