One day after being traded, Rea exited his start on Saturday with a right elbow sprain and was placed on the 15-day disabled list. The injury prompted the Marlins to inquire about a potential trade-back of sorts.
"Ultimately, we felt like the best thing was to try to work something out for both sides," Padres general manager A.J. Preller said. "When it was proposed Colin for Luis, that was a deal that we liked."
The Padres are adamant that Rea was healthy at the time of the trade. The Marlins had access to all of Rea's medical records in advance, and, like the Padres, they saw nothing wrong with his elbow.
The Marlins were frustrated that Rea was forced to exit his first start after just 3 1/3 innings. That prompted the two teams to open a discussion for a trade in which Rea would be returned to San Diego. Multiple other players and combinations were discussed, but the Marlins settled on Castillo.
"In the end, we just felt like it was in the best interest of both clubs to make the trade, Colin Rea for Luis Castillo, and move forward," Marlins president of baseball operations Michael Hill said. "I really don't want to get into his situation."
Preller was perfectly fine getting Rea back.
"When it was presented that we could get Colin back -- I said it publicly, I said it privately -- he was a very tough part in making the deal," Preller said. "… We think a lot of him. So when it was presented by the Marlins, and we had a chance to get him back, we were glad to do so."
Of course, the original trade centered on more than simply Rea and Castillo. Miami also received right-handers Andrew Cashner and Tayron Guerrero. In exchange, San Diego landed first-base prospect Josh Naylor, who slots into its system as the No. 4 prospect, reliever Carter Capps and right-hander Jarred Cosart.
The Padres weren't keen on giving up Rea in the first place, and they weren't actively shopping him until the Marlins asked. Preller said the two clubs had discussed "probably 75 different combinations" last week without Rea involved. Ultimately, Miami coveted him enough to demand his inclusion.
Although Cashner was the centerpiece of the deal, Rea was undoubtedly the toughest piece for the Padres to part with.
That's largely because Rea, a rookie with a 4.82 ERA in 20 appearances this season, still has five years of team control remaining. In that sense, San Diego's front office appears to be OK with having Rea returned.
"The hard part was parting with Colin Rea," said Padres manager Andy Green. "This was never anybody's plan, to trade him. In order to get that trade to go down, Colin had to be a part of it. So when we reacquired him today I called him on the phone and told him how excited I was."
Still, Rea is now dealing with elbow trouble -- though its extent remains unclear. He was slated for an MRI on Monday.
Castillo, meanwhile, is a 23-year-old flamethrower who was the Marlins' No. 15 prospect before the trade. He did not make an appearance in San Diego's system, but has a 2.25 ERA in 20 appearances for Class A Advanced Jupiter.
In terms of baseball history, a return swap of this sort is extremely uncommon, but it isn't exactly unprecedented.
On July 22, 2003, the Red Sox shipped Brandon Lyon and Anastacio Martinez to the Pirates in exchange for Mike Gonzalez and Scott Sauerbeck. But shortly thereafter, Pittsburgh began having concerns about Lyon's elbow.
Thus, on Deadline day, the Pirates traded Lyon and Martinez back to Boston, along with Jeff Suppan. The Pirates had Gonzalez returned -- and also received Freddy Sanchez. (Essentially, that turned the trade into Sauerbeck and Suppan for Sanchez.)
As the original Padres-Marlins deal stands now -- with Rea and Castillo factored out -- San Diego received Naylor, Capps and Cosart in exchange for Cashner and Guerrero.
"We did the deal and then Colin got hurt on Saturday night pitching for the Marlins," Preller said. "They brought it back to us and said, 'Hey is there a way to re-work the deal and a way to do something that makes both sides feel good?' … That's what we did."