It has happened a few times in football (soccer to the yanks), where a player is transferred between clubs. Not just any clubs though, lifelong hated rivals, which means that the player is villified for a long time afterwards.
It is usally made worse if the player is an icon or long standing player at the club.
This is inspired by the news that Wayne Rooney has decided he doesn't want to play for Man Utd anymore and is eyeing up a move to Man City next door. It would only be worse if he moved to Liverpool or Leeds, though neither of those two options is likely.
Ashley Cole, when he moved from Arsenal to Chelsea is another. Especially as he was complaining his wages (£50k per week) were not high enough.
Sol Campbell was another stalwart who played for Tottenham and then transferred to bitter rivals Arsenal. He was one of their best players and had been with them through the youth team and upwards. Then he decided he wanted a change. He was never welcome back at White Hart Lane, but instead collected several medals and a large salary.
So what other transfers have been between bitter, bitter rivals in other sports?