Every Wednesday, The Athletic’s MLB writers will be looking at a key what-if scenario from baseball’s history. This week: What would have changed if the D-Backs and Marlins hadn’t made a recent trade of two dynamic young stars?

In late July of 2019, as he was haggling with the Astros in an effort to trade ace Zack Greinke, Diamondbacks general manager Mike Hazen was working on something else seemingly contradictory. His club was a seller, the Diamondbacks having never joined the wild-card mix in earnest for the first four months of the season. But, as Hazen was selling with one hand, he was buying with another.

That same day, Hazen traded his top prospect. Jazz Chisholm had been signed for a song out of the Bahamas but had turned himself into an enticing combination of defensive skill at short and power potential at the plate. But Hazen and the Diamondbacks had their eyes on Marlins rookie right-hander Zac Gallen. Chisholm was the asking price. So, the same day Greinke was dealt, Arizona shipped away its top prospect to fill the “right-handed starter with the initials Z.G.”-shaped hole on its roster.

It’s hard to say it didn’t work out, no matter which side of the deal you were on. Gallen has been nothing but excellent for the Diamondbacks, posting a 2.85 ERA in 25 starts and finishing ninth in last year’s National League Cy Young voting. Though he’s currently out with a sprained elbow ligament, the damage is not serious — Gallen already is in the process of getting stretched back out and could return sometime in July. He is 25, has four more years of team control and has already has shown he can pitch like one of the best starters in the NL.

But the Marlins aren’t upset to have Chisholm, either. After struggling in his 21-game big-league introduction last season, the 23-year-old has given baseball fans a reason to watch the Marlins this year. Entering Tuesday, he was batting .263/.331/.474 with seven homers and a 122 OPS+. This year, only two pitches thrown at 100 mph or harder have been hit for home runs, and Chisholm smacked both of them. One of them was hit off Jacob deGrom. Chisholm has played mostly second, but now is getting his chance to handle short with Miguel Rojas on the injured list. He’s also swiped nine bags in 11 attempts.

Unwinding most trades doesn’t make for all that interesting an exercise. Sellers often need to sell or else risk seeing valuable players walk away for nothing. Buyers buy because they have roster needs to address. Many times, both sides would be worse off if they’d done nothing, no matter how good or bad the deal looks one, two, five or 10 years down the road.

But the Gallen-Chisholm trade — let’s say Jazz-Gallen, because that is more fun and makes it sound like a unit of musical measurement — doesn’t fit that narrative. The Diamondbacks weren’t clear buyers, yet they bought. The Marlins certainly weren’t in a position where they needed to trade a promising, cheap rookie starter. Which brings us to this question:

What if that trade never happened?

Erase that trade from history and the first thing we can say is that the Diamondbacks probably fade more quickly down the stretch in 2019, which could have carried steeper consequences for how the franchise operated in the following offseason.

After Gallen joined the Diamondbacks that year, he recorded a 2.89 ERA in eight starts before he was shut down midway through September to protect his arm. FanGraphs judged his contribution to be worth 0.8 WAR and Baseball-Reference valued it at 1.3 WAR. So, perhaps that means, instead of finishing with a surprising 85 wins — the result of a late push in September — the Diamondbacks would have finished closer to 84 or 83 wins.

But that also assumes that whoever would have been taking Gallen’s starts would have been replacement level, and given the quality of Arizona’s pitching depth that year, that’s a sizeable assumption. One of the pitchers to fill in for Gallen after he was shut down was Taylor Clarke, who was worth negative-0.5 bWAR in 84 innings. Chisholm was still at Double A, so he wouldn’t have made up the difference with his bat. Swap Gallen’s eight starts for eight of someone else from the Arizona system, and it’s possible the Diamondbacks might have finished at .500 or below.

What kind of repercussions would have followed that kind of record? That offseason, Hazen made a push. A team that was younger and cheaper had finished with a better record than the year before, despite not having the likes of Paul Goldschmidt, Patrick Corbin and A.J. Pollock. Hazen extended shortstop Nick Ahmed and left fielder David Peralta, both of whom were entering their final years before free agency. He splurged on Madison Bumgarner and Kole Calhoun on the open market, and traded two young but intriguing prospects for center fielder Starling Marte.

Those moves haven’t worked out — just check the standings from the last two seasons — and it maybe is a stretch to say that Hazen wouldn’t have felt so emboldened without Gallen. The Diamondbacks still would have been feeling good about their core of Ketel Marte, Carson Kelly, Christian Walker, Eduardo Escobar, Robbie Ray and Luke Weaver. Not having Gallen might have made a move like signing Bumgarner make more sense than it did at the time. But with Chisholm approaching the majors quickly, perhaps Hazen wouldn’t have made all of those moves.

Specifically, it might have made less sense to lock up Ahmed through 2023. Chisholm had been the heir apparent at short, but now he was in Miami. Arizona’s other great shortstop prospect, Geraldo Perdomo, had finished his season at High A and wasn’t going to be ready by 2020. Keeping Ahmed around to bridge the gap made sense. But if Chisholm was still a Diamondback, and on track to play every day in the majors by 2021 like he is now, it might have persuaded Diamondback management to let Ahmed walk in free agency. Depending on how much worse Arizona fared without Gallen in the rotation, it might even have persuaded them to trade Ahmed entering his walk year.

Would the Diamondbacks have been better off not making the swap? Meh.

It’s true that Ahmed’s deal isn’t looking great, considering that he’s 31, has a 70 OPS+, has dealt with knee problems and is owed more than $18 million over the next two seasons. It’s not a back-breaking deal, but it will make him harder to move now that the Diamondbacks are clear deadline and perhaps offseason sellers. They probably wouldn’t regret undoing that one.

But would avoiding a (relatively low-stakes) contract mistake be worth missing out on Gallen? Almost certainly not. He has pitched like an ace when healthy, and his recent health scares have been much less serious than initially feared. The prospect of Tommy John surgery will hang over most pitchers, especially ones who have already experienced elbow issues, which might lead one to prefer the high upside position player who is less likely to miss an entire year due to injury. But it’s hard to look at the way Gallen has pitched — with stuff and savvy and elite competitive fire — and say, “Excuse me, I would like to return this.”

The Marlins aren’t upset with what they got either. Would they like to have Gallen or any number of the exciting young pitchers they’ve dealt in recent seasons? Sure. But look at their rotation. Trevor Rogers will probably win Rookie of the Year. Pablo López and Sandy Alcantara have been great. Three of Keith Law’s top 100 prospects — including two in the top 25 — are Marlins pitchers who have yet to appear in the big leagues this year. What Miami needed more than another arm were exciting hitters at premium defensive positions. They needed someone like Chisholm.

The narrative of that trade may change as both Gallen and Chisholm progress in their careers. If Gallen’s elbow issues become recurring, and especially if they require surgery, Miami will look like the winner as long as Chisholm keeps things up. If Gallen keeps pitching like an ace and Chisholm falls off — he’s batted just .234 with a .670 OPS since returning from the injured list in mid-May, and his 34 percent strikeout rate is one reason the Diamondbacks felt comfortable moving him — the Diamondbacks will be able to claim victory.

But right now, it looks even. Chisholm swings and misses a lot, but being able to play the middle infield while turning around 100 mph heaters at the plate ain’t nothing. Gallen has been great but not consistently healthy, and he still hasn’t — partially because of the pandemic — pitched a full 32-start season in the majors. But each team got something out of the deal it didn’t have before.

Both teams have exciting young players around whom they can build for the next several years. Can they do so? Check the standings and you’ll realize that’s a whole other question.

(Photo: Christian Petersen / Getty Images)