The Giants acquired Mayer (forearm) from the Red Sox on Monday in exchange for left-hander Erik Miller and outfielder Carlos Gutierrez.
The Red Sox are selling low on Mayer, who has slashed just .223/.278/.346 in his first 364 plate appearances at the major-league level. He's just 23 years old and was considered an elite prospect not long ago, making Mayer a nice get for the Giants. On the shelf since June 26 due to a stress reaction in his left forearm, Mayer has resumed taking part in fielding drills and hitting off a tee and facing soft-toss pitching, but he remains without a timetable to return to game action. He could take over as San Francisco's everyday second baseman once he's back to full health.