Sports feed off the conflict bred from rivalries, and sports movies are no different. A great adversary or villain can take a good story and make it great, boiling the blood of viewers as the protagonist is foiled once more by his or her nemesis.
Imagine for a moment that this year's NBA Playoffs were a movie. It would have been a darn entertaining flick, but not just because of the level of play or the burgeoning crop of young superstars such as Derrick Rose and Kevin Durant.
No, the NBA had something it hasn't had in years—a great villain, this year played by LeBron James and the Miami Heat.
As I see it, a great villain has to be two things: adversarial to the protagonist in a manner that frustrates or enrages the viewer of the film, and well-crafted and nuanced so the villain is entertaining or believable.
Here come the bad guys.
(Note: These are taken from fictional films not explicitly based on real events, so no Jake LaMotta or Soviet hockey team here, folks.)