Chris Sale?
To me, it looked like the primary reason the White Sox unloaded this guy was the problems he was creating (blasting the front office over the Adam LaRoche debacle, destroying the entire team's promotional throw back jerseys right before a game).
Once the White Sox dealt Sale, they knew it ruined their chances to win and it set off the fire sale. But before all that, they had a very, very good team and could have easily competed for a title...