He couldn't have imagined that by day's end -- or by the seventh-inning stretch -- he'd be in the same boat.
While the White Sox were putting together their go-ahead rally to take the rubber game of their three-game series at Comerica Park, Tigers president/general manager Dave Dombrowski had just completed a deal for David Price aimed for October. One player, Drew Smyly, had already left the game, having thrown 95 pitches over five innings. The other was still in center field.
It was around 3:55 p.m. ET, five minutes before the non-waiver Trade Deadline. If the David Price trade was going to happen, Jackson had to be out of the game.
"Dave was right there in the dugout," Max Scherzer said, "and he's on the phone with the Commissioner's Office, and he's screaming, 'You've gotta get Austin off the field! You've gotta get Austin off the field!' So it was a Deadline deal."
Literally. The Tigers have made trades on Deadline day before, from the Jarrod Washburn trade in 2009 to the Sean Casey trade in 2006. Those, however, didn't happen midgame.
Likewise, while other deals have resulted in players being yanked -- Ubaldo Jimenez left his final Rockies start after one inning once Colorado had completed his trade to Cleveland on July 30, 2011, those didn't hit on Deadline.
So with a 2-2 count on Gordon Beckham and Joakim Soria trying to escape a bases-loaded jam, Rajai Davis came running out of the dugout toward center field as manager Brad Ausmus scrambled to halt play before Soria could throw another pitch.
With one hurried move out of the game, one of the core members of the Tigers' run of three consecutive American League Central titles saw his Detroit tenure suddenly end.
"That was the first time I've experienced anything like that," Justin Verlander said, "having to go get a guy because 4 o'clock's five minutes away and you can't risk having him on the field any longer to blow up an entire trade in the middle of an at-bat. It's pretty intense."
"At first, when I saw [Rajai] Davis running, I thought he might have been running in for Torii [Hunter]," said Castellanos, noting that Hunter had been hit by a pitch just below his left knee earlier in the game. "Then, when [Davis] went to center, I was kind of just confused, and then it kind of dawned on me that, 'Oh, crap, I think Jackson just got traded.'"
The one player that seemed to figure it out right away was Jackson.
"Once I saw Rajai come to the top step, I pretty much kind of knew what was going on," he said. "Just kind of a sad moment right there knowing that last run off the field, it was pretty tough with all your teammates that you played with."
Much of the sellout crowd of 41,306 at Comerica Park soon caught on. In the era of mobile devices and Twitter, word travels fast. So before Jackson even reached the dugout and received hugs from teammates, he received a standing ovation.
"It was kind of weird," Jackson said, "because I knew what was happening, but at the same time, I was in a daze a little bit. I really wanted to go hug all my teammates, really. But it is one of those situations where you don't know what to do. You're just stuck."
The feeling was emotional. While teammates were pumped about the prospect of David Price in their rotation, they were stunned at the departure of Jackson and Smyly. Usually, trades like these involve prospects, not familiar Major League players.
"I know we're getting David Price and he's a great pitcher and everything. But in this moment, it stinks," Scherzer said. "You have to remember, we're family in here. Austin and Smyly are part of this family, and we're losing two of our guys. I get that the guy who we're getting is very talented as well, but right now it stinks."
As Verlander put it, "There goes my brother running off the field. I know he's going somewhere else. You definitely have mixed emotions. I wish those guys the best of luck. They're two extremely talented players and extremely good guys. They'll be great."
Smyly had barely reached the clubhouse when he realized something was up.
"I came back to my locker," he said, "and my parents and a couple of my friends were kind of blowing my phone up, like, 'I think you're going to get traded.' And I was like, 'What? I don't know what you're talking about.' And then, sure enough, about 15 minutes later, it happened. Dombrowski called me in and told me.
"I get what they're trying to do. Price is outstanding. So, hopefully, it'll help them."
For Jackson, it hadn't sunk in, and he said it probably wouldn't until he put on a Mariners uniform alongside his old hitting coach, first-year Seattle manager Lloyd McClendon.
Smyly was numb as he talked with reporters after the game.
"Tampa is excited to have me, so I'm excited to be there," Smyly said. "A team that wants you is always nice, but this is all I know, so it [stinks] leaving."