At the time, the deal made a lot of sense. Reddick had been less than sensational in 2011 with the Sox, and Boston badly needed a closer with Jonathan Papelbon having taken a hike to Philadelphia.
Bailey had just completed his third season with the A's, during which he'd saved 75 games and had a 2.07 ERA.
It seemed to be a no-brainer.
But here we are in July. Bailey's been hurt and hasn't pitched all season. He'll probably still pan out in the long run, but so far his contribution has been zilch after having surgery on his right thumb.
And Reddick? Well, when the Red Sox last saw him as the calendar turned from April to May, he was just another guy in the Oakland lineup. He was batting third, sure, but he wasn't hitting like a No. 3 hitter should. He had four homers and nine RBIs. No big deal, right?
In the interim, Reddick has become a big deal indeed. He is in fact the biggest deal in the Oakland lineup day in and day out given that Yoenis Cespedes, the outfielder signed out of Cuba, has spent considerable time on the disabled list.
Reddick has 14 homers and 30 RBIs for the A's since the Red Sox last saw him, and if you want a bit of perspective on how good a performance that is, consider that the Next Great Thing in Boston, third baseman Will Middlebrooks, has hit 10 homers over the same span.
"I'm not a guy who likes to talk in terms of expectations," Oakland manager Bob Melvin said last week. "But there is no question that Josh has exceeded all the expectations we had for him.
"Based on what we'd seen about him before this and his numbers last year with the Red Sox [seven homers in 254 at-bats], you'd be looking at maybe a 15-to-20-homer guy. So for him to be out there with  already, that's saying something."
Andrew Bailey hasn't pitched since spring training for the Red Sox.
The fact is that Reddick has probably been the most valuable member of the Oakland roster this season. The feeling in the clubhouse is that he should have been the team's representative in the All-Star Game, although that honor ended up going to Ryan Cook, the first-year closer who replaced Bailey. The A's don't get many All-Star picks these days, and you have to go back almost a decade -- catcher Ramon Hernandez in 2003 -- to find the last position player wearing an Oakland uniform to represent the club.
Reddick doesn't seem much concerned with that. He's got a place to play every day, finally, and that's good enough for him.
"I didn't know what to expect when I got over here," Reddick said. "I'm just a guy who likes to go about my business and get out there and play. I've been able to do that here, and it's great.
"With Boston, that was a tough organization to do that in. Baseball's all about timing. I guess my timing is better here."
The No. 3 spot in the batting order is usually reserved for the team's best hitter, and for Oakland in 2012, that's mostly been Reddick. During his time with the Red Sox he was all over the place, mostly lower in the order. Last year he never batted in any of the top four spots, and 34 of his 64 starts came when he was batting seventh or eighth.
"I'm really happy to be in a key position in the lineup here," Reddick said. "To have them show me that kind of confidence is special.
"That wasn't happening in Boston. So to be able to come over here and fit in the way I have, that's great. It's worked out well."
It's certainly worked out for the A's, who didn't want to pay Bailey the kind of big money ($3.9 million) that quality arbitration-eligible players get. Reddick, who has two more years before he's arbitration-eligible, is making about one-eighth of that.
"Josh is a good player and a unique individual," Melvin said. "He's kind of a free spirit; he says what's on his mind. It comes out unfiltered, but in a good way.
"He's a good addition to our clubhouse; he brings some life in there that we didn't have before. He's a good teammate and a good player; you can't ask for anything better.
"More than that, he's been our most consistent player. He's been a great addition."
Of course, nothing is perfect. Reddick is finding that being in the lineup every day and being in right field every day has its drawbacks.
In April and early May, he opened some eyes with his throwing arm. He came into the weekend with seven outfield assists, but it kinds of bugs him. Runners have stopped challenging him.
"It's a mixed blessing," he said. "I like the fact that they're showing me respect by not running on me. But I really, really enjoy throwing runners out. I'm sorry now that I'm not getting as many chances as I was early in the season. Still, I guess it makes me happy to get that kind of respect."
Respect is a word that comes from Reddick in any conversation about his career.
You get the feeling he's getting more of it every day.