The A's acquired right-hander Sandy Rosario from the Red Sox for a player to be named later or cash considerations, the teams announced. In a related move, the A's designated outfielder Jermaine Mitchell for assignment.
Rosario, 27, has yet to appear in a game with the Red Sox, who claimed him off of waivers from Miami last month. He pitched in four games for this year's Marlins team, but spent most of the season in the minor leagues. He posted a 1.99 ERA with 8.2 K/9 and 1.4 BB/9 in 31 2/3 total innings for three of Miami's affiliates.
Mitchell, Oakland's fifth round selection in 2006, has yet to appear at the MLB level. The 28-year-old posted a .252/.345/.386 batting line in 474 plate appearances at Triple-A this past season.