Rosario is a 27-year-old reliever who has spent most of his time in the minor leagues. He has appeared in only 7-2/3 innings over three years in the majors, allowing 13 runs and 22 hits with four strikeouts in 10 appearances. Rosario spent the majority of the 2012 season with Triple-A New Orleans, pitching 26 total innings with a 1.04 ERA and 22 strikeouts. He was called up to the Marlins in June and pitched three innings over four games, but was sent back down and did not receive a September callup.
To make room for Rosario on the roster, the Red Sox designated outfielder Che-Hsuan Lin for assignment. Lin, 24, made his first major league appearance in 2012. He made 12 plate appearances in nine games with three hits, one run, and five strikeouts.