The Padres Bet on Trevor Rosenthal’s Resurgence

The San Diego Padres came into 2020 with one of the best late-inning setups in baseball. Their plan was simple: offseason acquisitions Drew Pomeranz and Emilio Pagán would handle high-leverage situations in the middle innings before passing the baton to Kirby Yates, one of the most dominant relievers in the game. That plan hasn’t worked out this year, largely because Yates will miss the rest of the season after surgery to remove bone chips from his elbow. On Saturday, however, they made a move to replenish their planned area of strength, acquiring Trevor Rosenthal in a trade with the Royals.

Nationals fans might wonder whether acquiring Rosenthal is supposed to be a good thing. He was, no doubt, abysmal for them last year — he racked up a 34.9% walk rate over 12 games before getting the heave-ho. A slightly longer stint with the Tigers ended the same way — striking out 28.6% of the batters you face is good, but not when you’re walking 26.8% of them as well. The Royals signed him as a reclamation project, nothing more — a minor league deal that could escalate to as much as $4.25 million based on incentive bonuses.

Consider him reclaimed. In 13.2 innings this year, he’s been effective, striking out 37.5% of his opponents en route to a 3.29 ERA that, while still short of his peak, represents a huge improvement from last year’s disaster. It’s not all daisies and lollipops, even at surface level — he’s walked 12.5% of opposing batters and given up two home runs. Mid-three ERA relievers don’t grow on trees, though, and San Diego was intent on getting one.

In acquiring Rosenthal, the Padres are making a bet that they can fix him, because despite his acceptable results this year, there are worrisome underlying signs. As Johnny Asel pointed out, Rosenthal might resemble his St. Louis form superficially, but the way he’s doing it has changed completely. He’s flooding the center of the strike zone and daring batters to hit it, which explains the better walk rate but also the hard contact.

At his peak, Rosenthal was that most cherished baseball stereotype: effectively wild. He lived on the edges of the strike zone and just outside it. That ballooned his walk rate, but it also suppressed home runs; squaring up Rosenthal’s explosive fastball and where’d-it-go changeup was simply beyond most batters when he didn’t leave them hanging over the plate.

To wit, when batters swing at pitches he leaves over the heart of the plate, per Baseball Savant’s definitions, they’ve hit nine home runs in 774 swings. When they swing at pitches on the edges of the plate, they’ve hit two in 816 swings. That’s not wildly different from how major league pitchers work in general — Rosenthal suppresses home runs in a similar ratio in both places — but for a pitcher who will always allow some traffic on the bases due to his walk rate, home runs are an anathema.

Last year, Rosenthal didn’t throw many pitches in the heart of the plate, because he didn’t throw many pitches in the strike zone. He threw a career-low 24.4% of pitches there. This year, he’s thrown a career-high 33% of pitches over the heart. Can’t locate? Jam everything over the center and pray:

Needing to huck the ball right over the middle of the plate to throw strikes is hardly optimal, and it’s a tough problem to solve. Your first thought might be that he simply needs to get his mechanics down and start repeating his delivery more; it was certainly mine. Compare 2020 to 2017, his last effective season, and you’ll hardly see that, however.

Imagine all of the release points for fastballs Rosenthal threw in 2017 as a cloud. He obviously can’t release his pitch at the exact same point in space every time, so every pitch is some distance away from the center of that cloud. In 2017, his release point was 4.5 inches away from the exact center on average. In 2020, it’s two inches away on average. He’s actually tightened the degree to which he repeats his delivery!

Notably, however, he’s also changed where that center of mass is. He’s releasing the ball six inches closer to home plate, on average, than he did from 2015-2017. It’s not evident in his mechanics, at least to my eyes, but that’s at least something the Padres could look at. Here he is in 2015 releasing a fastball to a righty:

And again in 2020:

Could the camera angle and zoom be disguising a change? Maybe! I don’t really see one, though, and it would hardly surprise me if Rosenthal’s control issues are simply rust. After all, he’s still faced only 141 batters in major league games since his surgery. It would hardly be surprising if he still had some kinks to work out. He’s repeating his delivery well right now; that delivery just ends in a slightly different place than it did before, and maybe that’s confounding his ability to hit his spots.

Even if this new Rosenthal is here to stay, if there’s no returning to his prior unhittable self, it’s hardly the end of the world. He’s getting swinging strikes 14.2% of the time and inducing chases at a career-high rate when he misses the zone. A lot of that comes down to throwing his slider more often (24% of the time as compared to 13% in 2017) in lieu of a mixture of fastballs and changeups. He’s still inducing whiffs on 30% of swings against his fastball, as well as a gaudy 60% against his changeup, long his signature weapon.

That’s the pitcher the Padres paid for — a reliever who can fake being the best guy in your bullpen but is better suited in a support role. He should slot in alongside Pagán and Pomeranz, though Pomeranz will likely get the first shot at anchoring the unit. And there’s upside, too: if he can start to hunt corners again, well, Rosenthal was one of the best relievers in baseball in St. Louis, and it’s certainly not out of the question that he could regain an approximation of that form.

For that bullpen upgrade, the Royals received an interesting return. Edward Olivares is the kind of prospect the Royals have historically coveted: he has plus straight-line speed and good instincts on the basepaths, and you can dream on his athleticism helping his other skills play up. He has also posted mid-teens home run totals for three straight years, though we remain skeptical that he’ll be able to translate that power to the majors. If the power doesn’t translate, he still projects as a fourth outfielder, acceptable defensively in center and a plus in the corners. He scuffled in limited playing time in the majors this year, but his underlying numbers look totally fine, and that surely didn’t figure into either side’s evaluation of the deal. He’ll slot in at 27th on the Royals’ list after this trade.

With Trent Grisham ensconced in center field, the Padres hardly needed Olivares this year, and they’re facing a 40-man roster crunch this offseason. This makes trading him more palatable; with limited space, they weren’t going to be able to protect everyone anyway, so losing Olivares lets them hold onto someone else. That doesn’t fully offset the cost, as Olivares is a better bet to contribute than whichever extra marginal prospect they’re able to protect, but it’s still an extra carrot in this trade.

The Padres are also sending a player to be named later in the deal. It’s been reported this PTBNL will be a low-level relief prospect. I asked professional knower of prospects Eric Longenhagen what that entailed, and he deduced that it was likely a pitcher who would need to be added to the 40-man either this year (Michell Miliano?) or next (any number of young Latin American arms, or perhaps a prospect whose development was slowed by injury like Dylan Coleman).

Rosenthal’s strike-throwing and bat-missing prowess will determine whether this trade gives the Padres what they need. Whether he works out or not, however, this is exactly the type of trade they should be trying to make. It doesn’t cost them nothing, but fringe 40-man names are their biggest logjam right now, which vastly reduces their marginal cost. Not only that, if it does work out, their potential returns are huge. If Rosenthal is still rounding into form and has another gear, he’s an impact acquisition. If this is it, he’s an innings-eating bullpen arm. That’s two ways to win, and San Diego paid a reasonable price for it.

As for the Royals, they signed a small contract to take the bet that Rosenthal would rebound enough to be traded. They won! Edward Olivares-level prospects don’t grow on trees, and without any urgency to win rightthissecond, they can discover what they have in him more easily than the Padres could have. This is the second deal the teams have linked up on this season, after an earlier swap of Tim Hill for Franchy Cordero and Ronald Bolaños. It’s easy to see why — the teams’ different timelines make for perfect trade partners, and both squads should be quite happy with this one.