since it has to be a sports star, it'd be donovan mcnabb. Most over-rated "star" in the sports business. 2nd goes to vince carter for not giving a crap for 80% of his games.
If it'd be a non-star, it'd be every athlete who only tried during their contract year. After that, they just gained weight, got injured, or just didn't give a damn about ripping teams off.