Rosario's contract was purchased by the Red Sox on Friday.
Acquired from San Diego in the Mitch Moreland trade, Rosario is one of the best athletes in Boston's farm system, but his game success has been lacking against more advanced pitching. The 21-year-old outfielder is a plus runner with a very passive approach at the plate that has led to high walk rates and very limited power output. He could open the year at High-A or Double-A.