The Giants acquired Mayer (forearm) from the Red Sox on Monday in exchange for Erik Miller, Ken Rosenthal of The Athletic reports.
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 and was considered an elite prospect not long ago, making Mayer a nice get for the Giants. Mayer has been sidelined since late June with a stress reaction in his left forearm and remains without a timetable. He could take over at second base for San Francisco once he's ready physically.