I think Jimmy Foxx could be considered to have contributed something substantive to the RedSox .. 5 time All Star with three top 10 MVP finishes - including MVP in 1938 - the year of the 175 RBI.Connie Mack dismantled a great As team and sold a bunch of very good older players off to other teams, presumably to save money. The three HOFers he sold - Foxx, Lefty Grove, and Mickey Cochrane - were pissed. More or less as punishment to Mack, they chose to wear the caps of the teams they went to (Sox, Sox, and Tigers, respectively).
From a stats perspective, only Grove did anything of substance on the destination team. But all three would definitely wear As caps under the current HOF regime.
edit: forgot link:
http://www.baseball-reference.com/players/f/foxxji01.shtml