The Red Sox have acquired Mike Carp from the Seattle Mariners, per a release by Boston. Rather than send a player over, Boston agreed to send either cash or a player to be named later to Seattle, as the Mariners 40-man being full is what prompted Carp's designation in the first place.
Ryan Kalish was moved to the 60-day disabled list in order to make room on the 40-man roster, so the Red Sox do not need to designate any of their own players in order to bring Carp aboard. However, this does mean that an easy roster spot for either Ryan Sweeney or Lyle Overbay no longer exists, unless someone else requires the 60-day DL, or Carp fails to make the team out of spring training and is waived.
The left-handed Carp has hit just .255/.327/.413 in his career, but played well in 2011, when he managed a 125 OPS+ in 313 plate appearances. The hope is that Carp, free from pitcher-friendly Safeco, will produce more consistently. As his approach is questionable, though, with a bat that doesn't project well against better pitching, that might just be a dream. Luckily, the Red Sox won't be relying on Carp for much more than a bench presence, as someone who can suit up for duty in either left or at first base if and when necessary. The fact he has hit lefties better than righties in his career despite his handedness makes him an odd fit for Boston's bench, given the presence of Jonny Gomes and Mike Napoli's handedness, but maybe the Sox scouts and coaching staff believe they can do a better job with his development than the Mariners have. Given Seattle's role as one of the worst offenses in the game over the past few years, it's not a bad theory to attach to a bench player.
What this means for Lyle Overbay, who signed a minor-league deal with Boston in the hopes of playing somewhat often, is unknown. He can opt-out if he doesn't make the big-league roster at the end of spring training, and unless Carp fails to make the club, that's a likely scenario. However, it's also possible a deal could be worked out with the Brewers, who need a first baseman now that Mat Gamel is out for the year with a torn ACL, and were hoping to sign Overbay before the Red Sox got to him in the first place. That's all hypothetical, though.