D-Backs Sign Héctor Rondón, Who Might Be Good

Héctor Rondón made a ton of appearances last year for a solid Houston bullpen. The Astros had a top 10 bullpen in both ERA and WAR, and Rondón made the third-most appearances on the team. If you only knew those two things, then, it would look like quite the deal when the Diamondbacks signed Rondón for a mere $3 million, with a club option for 2021 tacked onto the back end, as Nick Piecoro reported yesterday.

Of course, I cleverly avoided telling you anything about how good Rondón was last year aside from his appearances. And while he wasn’t abysmal, at least not completely — he had a 3.71 ERA, racked up positive WPA, and still sat 97 mph with his fastball — some of the underlying metrics looked rough. His FIP was a career-worst 4.96, his strikeout rate cratered to 18.7%, and he was below replacement level on the year in our FIP-based WAR accounting. By the playoffs, he was buried in the bullpen — seven relievers in the Houston ‘pen faced more batters, and his average entry leverage was a piddling 0.16.

So before we decide if this was a good signing for the Diamondbacks, we need to decide if Rondón is still good. At his peak on the Cubs, he was an impact reliever with pretty good stuff and great control. He’s still only 31 — this isn’t some kind of Fernando Rodney situation here, where there’s a picture in his attic with an increasingly tilted cap that keeps him in baseball shape. He’s still, age-wise at least, in his prime.

So what’s changed for Rondón? We can rule out the normal way relievers break. He’s been extremely durable, making at least 50 appearances for six straight years. He hasn’t lost velocity, either: he throws as hard now as he did when he was on the Cubs. And his postseason banishment wasn’t a matter of him losing steam at the end of a long slog of a year; his fastball averaged 96.8 mph in the playoffs, barely down from 96.9 during the regular season.

Did his trusty slider fall off a cliff? Not really — he threw it roughly as often as ever, and its velocity and movement were essentially unchanged. It missed a few fewer bats, to be sure, but not catastrophically so, and batters didn’t do much with it when they did connect. His changeup looked bad — but honestly, his changeup has always looked bad. He throws it sparingly, and that’s no accident.

Still, Rondón got a lot worse at missing bats in 2019. His 9.8% swinging strike rate was significantly below league average, the first time he’s done worse than the league at missing bats. His contact rate, too, spiked to a career high. Batters simply stopped missing his pitches, and in homer-happy 2019, that’s not where you want to be.

So what gives? We could get Sherlock Holmes on the case — but luckily, we won’t have to, because every two-bit analyst, as well as many fancy analysts, have already solved this one. It’s the sinker, stupid.

The sinker is much-maligned, sometimes without reason — but in Rondón’s case, it sure looks bad. His carrying tool has always been a riding four-seam fastball. Used right, it explodes through the top of the strike zone, befuddling hitters. He hasn’t always had the best command of the pitch (hey, he’s a reliever!), but its velocity and movement have been enough to keep batters off-balance.

Before 2019, that was basically Rondón’s game. Throw the four-seam to bully hitters, then hit them with the slider when they were looking fastball. It’s quintessential modern baseball, very much a min-max approach to pitching. And then in 2019, he changed:

It’s not as though he’d never thrown a sinker before; he’d dabbled in two-seam sorcery with the Cubs, only fully buying into the four-seamer as his weapon of choice in 2016. Not coincidentally, 2016 saw a spike in his strikeout rate. That’s not to say that there were no costs; Rondón’s groundball rate declined, and more fly balls combined with a spike in HR/FB% bit him. But HR/FB% isn’t very stable, and for the most part the tradeoff worked; he struck out more batters than ever before by using his best pitches more often. MVP Machine sequel, here I come.

Of course, the story doesn’t end there. Rondón never completely scrapped his sinker; he merely cut down on its usage. He used it sparingly, opportunistically; in the first pitch of at-bats to throw hitters off the scent, or when batters were ahead, when they were least likely to swing at a new-look pitch. It wasn’t a two strike pitch, of course, because people don’t swing and miss at sinkers very much, but it was a splash of color, a tiny bit of spice in an otherwise meat-and-potatoes pitch mix.

But then something terrible happened. The sinker was good in 2018! It didn’t miss a lot of bats — let’s not go crazy — but he was able to sneak the pitch by for a strike somewhat often, and batters didn’t crush the pitch when they did swing.

Come 2019, there was a new plan. Get behind to a righty? Hit them with the sinker. He threw the pitch a full quarter of the time when behind in the count to right-handed batters, up from only 6% in 2018. And, uh:

Look, these samples aren’t robust. He’s a reliever, and it’s just one handedness split after one count, and it’s something like 50 batters a year. I get all that. But it’s a serious problem. And that walk rate? It’s no fluke. Rondón hit the zone with only 55% of his down-in-the-count sinkers in 2019, as compared to 65% with his four-seamer. That leads to falling behind in the count more. And when he did throw it in the zone, batters weren’t fooled — they swung 82% of the time, against 73% for the four-seamer.

Put it all together, and the picture is ugly. Rondón found a new pitch that he mainly used when falling behind to right-handed batters. That pitch didn’t hit the strike zone much, and when it did, righties always swung — literally always. It was also a high-contact pitch, so he was stuck between a rock and a hard place. Miss the strike zone, and it was probably a ball (batters swung only 35% of the time in this situation, overwhelmingly at pitches on the border of the zone). Put it in the zone, and it was probably in play. The extra balls led to more walks, and the contact suppressed his strikeouts.

In fact, Rondón’s habitual domination of righties showed some worrisome cracks in 2019. He had a lower strikeout rate against righties than lefties, nearly unheard of for a fastball/slider reliever. He had a higher walk rate against righties. He got worse at recovering within a plate appearance: when he fell behind in the count 1-0, he struck out only 12.9% of batters while walking 12.9% as well (for his career, he’s at 17.8% strikeouts and 11.5% walks in that situation).

If I were the Diamondbacks, I’d tell Rondón to cool it with the sinker. If we’re being honest, it wasn’t good when behind in the count even in 2018 — batters swung at all seven sinkers he threw in the strike zone and didn’t miss any. It worked slightly better on the first pitch, as he was able to sneak in strikes here and there, but it still wasn’t gangbusters.

It’s not actually that easy to convince pitchers to change. The Astros are the masters of pitch arsenal design, and they couldn’t prevent this from happening. Heck, maybe I’m missing something, and he actually had to go to the sinker to keep batters from sitting on his other two pitches. Maybe this really is the best form of Rondón.

But I don’t think so. I think that if he simply goes back to what he was doing before 2019, he’ll regain a lot of effectiveness. If he can do that, he’ll slot in right next to Archie Bradley and Andrew Chafin to form an effective bullpen trio.

And the Diamondbacks need that. Short of cloning Bradley and calling the clone Braddie Archley to throw ethics investigators off the scent, they probably won’t have a great bullpen in 2020. There will always be surprises, of course, but it’s probably optimistic to expect great seasons out of 2019 pop-up sensation Kevin Ginkel, perpetually meh Matt Andriese, are-you-sure-this-guy-exists minor league depth piece Stefan Crichton, or even actual prospect Yoan López.

That list is also the reason that signing Rondón isn’t without its downsides. Relievers are volatile, sometimes wildly so, and using a roster spot on a 31-year-old leaves you a lot less space to test out the Kevins Ginkel and Stefans Crichton of the world. And it’s not as though the team is getting a proven stopper in the deal — he was literally below replacement level in literally 2019.

But for a team on the cusp of the playoffs, I’m into the decision to look for at least a little bullpen stability. I think Rondón can get back to his former self, and for $3 million plus a discounted look at 2021, that’s a gamble I’d be willing to take. I’ve really liked the Arizona front office’s plans the past two years, and this move is no exception.