MLB Mock Blockbuster Trade: Arizona Diamondbacks Deal Merrill Kelly to Cardinals

Two of the bigger question marks around the 2025 MLB trade deadline are what the St. Louis Cardinals and Arizona Diamondbacks will do.

Are they both buyers? Will they each sell? Or could one sell and the other buy?

All of that is possible, including a trade between the two teams.

If the Cardinals buy at the deadline, they are likely to be interested in adding a starting pitcher. The Diamondbacks could trade a pair of starters set to be free agents after the season.

On July 2, ESPN's David Schoenfield connected the Cardinals to Diamondbacks right-hander Merrill Kelly.

"The Cardinals continue to exceed expectations, and Kelly's $7 million contract would be especially attractive to them -- or any team looking for a starter at an affordable rate, for that matter," Schoenfield wrote. "As for the need: The Cardinals rank in the middle of the pack in the majors in rotation ERA, but Erick Fedde, Andre Pallante and Miles Mikolas are averaging fewer than 6.5 strikeouts per nine. (St. Louis is 26th in rotation strikeout rate.)

"Kelly would give them a better strikeout pitcher to go alongside Sonny Gray to head a potential playoff rotation."

Let's continue to take a look at a potential Kelly trade to the Cardinals.

Arizona Diamondbacks-St. Louis Cardinals Mock Trade

Arizona Diamondbacks receive Cardinals No. 16 prospect and right-hander Gordon Graceffo and Cardinals No. 22 prospect and outfielder Matt Koperniak.

St. Louis Cardinals receive right-hander Merrill Kelly.

Trades involving the Diamondbacks and the Cardinals are the theme of the day. On Tuesday, I also mocked Diamondbacks starter Zac Gallen to the Toronto Blue Jays and Cardinals relief pitcher Ryan Helsley to the Philadelphia Phillies.

In this trade, the Diamondbacks still sell. If they are going to move on from Gallen, they might as well also trade Kelly. Both starters will be free agents this winter.

Should the Cardinals elect to buy, Kelly would be a great addition. At 36 years old, he's not going to be a huge difference maker, but he's a reliable, experienced starter who pitched wonderfully in the only postseason opportunity he's had in his career.

"Kelly is the type of pitcher who used to be called a bulldog. He battles, he's tough, and he gets the most out of an arsenal that features a pedestrian 92 mph fastball," Schoenfield wrote. "Every team would love to have him in its rotation and, for what it's worth, he was excellent in the 2023 postseason for Arizona when he posted a 2.25 ERA across four starts.

"He had a nine-run blowup in his second outing of 2025 but is pitching better than ever since then with a 2.83 ERA and more strikeouts than innings pitched."

Overall this season, Kelly is 7-4 with a 3.55 ERA, 1.087 WHIP and 103 strikeouts in 104 innings. Including 2025, he's held an ERA between 3.25 and 3.60 in three of the past four seasons.

Kelly could also potentially benefit from not pitching his home games at Chase Field. In 10 home starts this season, the right-hander has yielded eight home runs.

In general, Chase Field is a hard place to hit a home run. But because of the higher home-run allowed rate, opposing hitters have an OPS 72 points higher versus Kelly at Chase Field than all other ballparks combined.

Interestingly, despite allowing more bombs in home starts this season, Kelly still has a better ERA at Chase Field than on the road. But at Busch Stadium, Kelly could yield fewer homers and perhaps be even more productive for fantasy managers.

With Graceffo and Koperniak, I kept the theme of Arizona landing near-ready prospects in return for their starting pitchers. Graceffo and Koperniak have each mostly played at Triple-A this season.