Why Red Sox are trading Marcelo Mayer to Gaints for Erik Miller

The Boston Red Sox have been making some massive moves at this year's trade deadline, acquiring Curtis Mead in one deal, and later Adley Rutschman on deadline day.But one of the more unexpected moves came a little later, under an hour before the deadline passed. According to Ken Rosenthal of The Athletic, the Red Sox are close to trading away Marcelo Mayer in a deal with the San Francisco Giants.In this reported trade, the Red Sox would be getting back reliever Erik Miller. It's a massive trade, with Mayer, a former top prospect for the Red Sox, headed to the Giants. But why did they make such a bold move with Mayer when they didn't have to?Why Red Sox are trading Marcelo Mayer to Giants"Giants closer to acquiring Marcelo Mayer from Red Sox for reliever Erik Miller, sources tell me and And