Mark Kotsay has filed for free agency, becoming the seventh member of the Red Sox to test the waters this offseason. Kotsay became a vital member of Boston's lineup down the stretch and in the postseason, especially after Mike Lowell went down with a hip injury. He would prefer to be a starter, which could prevent him for returning to the Red Sox, who acquired Kotsay from the Braves in a waiver trade on Aug. 27.