Crain had played in Chicago for two-and-a-half seasons, playing for the cross-town White Sox. He was in the middle of his best year ever in 2013 before a strained right shoulder suffered in June cut his season in half. Up to that point, he made 38 appearances and posted a 0.74 ERA and 1.15 WHIP while striking out over 11 batters per nine innings.
The White Sox traded the injured Crain mid-season to the Tampa Bay Rays, when it was still thought he was close to healthy. However, he never pitched an inning for the Rays.
In the two years with the White Sox prior to 2013, Crain combined for a 2.54 ERA and 1.17 WHIP with over 10 strikeouts per nine innings.
The Cubs, meanwhile, are losing closer Kevin Gregg to free agency and have a fairly weak back of the bullpen. Blake Parker and Pedro Strop were the only other truly effective relievers on the team last year as the team's relief corps posted a 4.04 ERA, sixth-worst in the MLB.