Rosario, 27, a native of the Dominican Republic, became Red Sox property again Monday when they claimed him from the A's. Oakland designated Rosario for assignment on Nov. 30.
Rosario's travels began in mid-October. The Red Sox on Oct. 17 claimed Rosario from the Marlins, the organization he had been with since signing a pro deal in July 2004.
When the time came for the Sox to set their 40-man roster in November, they designated Rosario for assignment before working out a deal with Oakland. Boston received right-hander Graham Godfrey as a player to be named.
That trade was on Nov. 28. Two days later, Oakland designated Rosario again, and Boston still had interest.
Rosario spent most of 2012 with Triple-A New Orleans in the Marlins' system, posting a 1.04 ERA and 16 saves in 25 relief appearances. He allowed six runs in four relief appearances and three innings with the big club this season. He made two appearances in the Majors in 2010 and '11.
Boston's 40-man roster is at 39.