http://sportsillustrated.cnn.com/vau...ine/MAG1153364
According to SI, 78% of NFL players are either bankrupt or under financial stress within two years of retirement. I did not see a definition of "financial stress" in the article.
Keep in mind that most NFL players don't make enough money to truly "retire" on, and a lot of them are probably not going to find well-paying jobs. So unless someone has done a study of the top-tier players, these statistics would be highly suspect if applied to the guys who've made millions playing football.