Jason Ross

Ryan Zeferjahn, acquired by the Cubs during their mad dash before the 2026 MLB trade deadline, is a lot of things. He's a fireballer; he's a wild man; he's a freak; he's an alien. Whatever you want to call him, he's an outlier of a baseball player. The Cubs acquired some names who are more familiar than Zeferjahn. Kevin Gausman, for example, has been among the best starters in baseball for half a decade. But no player may have a bigger impact on a per-inning basis than their new weapon out of the bullpen—that is, if the Cubs (or any team) can learn how to tame the beast. Let's start with the elephant in the room: this dude walks people. He's walked people since he was back in college, so it's nothing new. Baseball America, in his 2019 draft profile, highlighted his propensity to vacillate between striking hitters out and walking them. "Two weeks before striking out 14 against the Longhorns, he walked seven hitters in six innings against Baylor," they noted. I'd love to tell you this has gotten better over the years, but since coming up in 2024 with the Los Angeles Angels, he's got the third highest walk rate in baseball among pitchers who have thrown at least 125 innings. This year, he's walked 14.3% of his opponents. Strangely enough, it just might not matter. What makes Zeferjahn an alien is his fastball. This is a special pitch. What makes it so special is how he spins it; it's incredibly inefficient. We're programed to have a negative connotation with things that are inefficient, but with pitches, it's not necessarily a bad thing. In layman's terms, low efficiency means more cut and less backspin. We live in a world in which velocity is king, but as everyone chases every last mile-per-hour, things become more normalized. Throwing 97 MPH today just isn't special. You have to stand out in some other way. I'll borrow a line from Kevin Goldstein to highlight this: "The further one can get from the norm, the more effective the pitch can be beyond just the pure speed. Hitters expect a fastball to behave a certain way out of the hand and when it doesn’t, regardless of the direction in which it deviates, it creates challenges in terms of making hard contact, or any contact at all." SzRCRFJfWGw0TUFRPT1fQWdVSFVsWURVMVlBWFZaVUF3QUhBZ0lDQUFOWFd3VUFVMU1DQ1FGVVVBTUdCd2NF.mp4 What Zeferjahn does with his fastball's shape makes it special. He throws a relatively low-slot fastball with inefficient spin. The result is that the shape of the pitch is elite: his Stuff+ on the pitch ranks top-10 in baseball (relievers only), ahead of Jeff Hoffman, Tanner Scott, and Louis Varland. To highlight how his slot and spin rate help create this, let's compare his fastball to another pitcher's which seems similar on the surface, that of Pirates righty Jared Jones. Jones and Zeferjahn have similar RPM on their fastballs and have similar velocities (though Jones does throw a little harder). In theory, you'd think they would have similar Stuff+, but they do not. Jones's fastball clocks in with FanGraphs's Stuff+ model as a 92, while Zeferjahn's is a 120. This is vastly different. Jones gets great results on the pitch, so this isn't a dig on Jones, but Zeferjahn is on another planet. He leads on Whiff% (41.1% versus 24.9%), and he's given up just four hits all season to the tune of an absurd .087 batting average. If you're worried he's getting good luck, don't fear. His xBA on the pitch is just .105. Like I said; he's a freak. The Cubs adore low-spin-efficiency fastballs. While he's not as inefficient as Cade Horton (who is under 80% in terms of active spin), he's definitely in the correct organization—one that really targets this pitch. We have seen firsthand what the Cubs could do on the fly with Horton, adding a sinker and using his cut-ride fastball to really attack hitters in interesting ways. It's not hard to think what the Cubs could do with their new toy, or that the Cubs may be in a better position than the Angels to get the most out of it. What's shocking is that his fastball might not even be his best pitch. You could make a compelling argument that his sweeper, which he throws roughly a third of the time, is just as good, or better. That pitch boasts an impressive 118 on FanGraphs's Stuff+ model, and also sees hitters whiff on it over 40% of the time. He has two plus-plus offerings in shape and production. Again: it's special stuff. Zeferjahn isn't just an alien on the mound with the stuff he's capable of throwing at a hitter, he's a statistical freak as well: he has a 96th-percentile whiff rate and just a 2nd-percentile chase rate. That's unfathomable. What it means is that if the guy can just throw enough strikes, no one is going to touch him. We can see that because, even when hitters do make contact, his batted-ball data against is pretty good, too. If you want to dream as to what could be, look no further than his last 16 innings, because there's a chance something has just clicked, and there's some data to support that it might not be smoke and mirrors. Over his last 16 innings, Zeferjahn has just four walks. Over his last 10 innings, he has walked just one hitter. Interestingly enough, the walk he had was called a strikeout on the field. The Giants' Grant McCoy had to use an ABS challenge to even get the walk. What's the change? His release point—which has moved because he's slid toward third base in his setup on the rubber, and is striding slightly more closed. On the left is Zeferjahn in April; on the right is him last month. This is a major departure in his motion and seems to correlate with his improved walk rate. It's too small of a sample to say "mission accomplished!" and that everything is fixed, but when we see outlier data coupled with a noticeable change, it makes you feel like there's a reason behind the improvement—and that it could therefore be sustainable. He's on a better line to tunnel his stuff and to keep it on the plate, and lo, everything has changed for the better. Over that span, it's not just the walks that are improved; he's absolutely dominating hitters. Since June 23, the righty has struck out almost half the hitters he's faced. This is Mason Miller levels of dominance. In his last outing as an Angel, he managed to strikeout four Brewers in a nearly perfect five-out performance. It's easy to imagine how much fun it could be seeing him do that to Milwaukee at Wrigley. All of this leads me back to my premise; this guy is an alien. He's unique. He has a great fastball that highlights its odd, inefficient spin and low arm slot. He's a whiff merchant, even while generating almost no chase. He used to walk everyone, but lately, he can't walk anyone. There just aren't many pitchers like this in baseball. The upside is massive; the risk is real. But he's a unique player, and one who could slot into a Cubs bullpen for years to come—because the best part about Zeferjahn is that despite being 28 years old, he's a late bloomer and won't hit free agency until November 2030. There's a good chance that one of the most unhittable pitchers in baseball will be shutting teams down for the Cubs for quite some time.