Daniel Bard was one of the best relievers in baseball between 2009 and 2011. In those three years, mostly serving as a setup man for closer Jonathan Papelbon, Bard threw 197 innings and posted a 2.88 ERA. He struck out over a batter an inning and allowed only 6.0 hits per nine innings. His walk totals were a little high, but nothing terrible at 3.5 per nine innings.
Then came last season. Bard was really bad. The Red Sox had moved him into the rotation and he floundered. He allowed more than a hit an inning. His strikeout numbers were almost cut in half and he was walking more batters than he struck out. The Red Sox moved him back to the bullpen, but things got no better there. They sent him down to the minors and his control completely abandoned him. In 2012, he walked almost a batter an inning in the minors. Things got even worse this year. So when the Red Sox needed to open up a roster spot for newly-acquired outfielder Quintin Berry, they designated Bard for assignment. That's where the Cubs claimed him today.
Obviously Bard is very familiar to Theo Epstein and Jed Hoyer and they believe they have a shot at returning Bard to the level he was at when they ran the Red Sox organization. When he pitched there, he could hit 100 mph on the radar gun. These days, he pitches more in the low 90s, although he occasionally flash a taste of the old heat and reach 96 or 97. He still can't hit the plate. He had a wipeout slider in his heyday. It still moves, it just doesn't move over the plate.
If the Cubs can fix Bard and return him to where he was from 2009 to 2011, obviously the Cubs will have gotten a major talent for nothing. I don't want to cite WAR much, but according to Baseball-Reference.com, his WAR in 2010 alone was 3.1, For a reliever, that's incredible. It they can't, they won't have lost much.
The Cubs will have a herculean task ahead of them trying to get Bard back to where he was in 2011. You can google "Daniel Bard Fix" and you'll find hundreds of articles from writers on the Red Sox about their efforts to get him back to where he was. Maybe Theo Epstein knows something that the Red Sox don't. More likely, he figures the potential upside against the cost is too great to pass on, even if the Cubs don't know how to fix him at this time.
As an added Cubs connection, Bard is the cousin of Tennessee Smokies outfielder John Andreoli.