I clicked "other" because of a book I've been reading by Dan Moldea. Moldea is a well known investigative reporter. It is called "Interference -How Organized Crime Influences Professional Football". A lot of his research in the original version of the book dealt with racketeering and he demonstrates that it did indeed influence the NFL in the old days. Now, with legalized gambling in so many states he says the influence has shifted away from the gamblers. He now makes a strong case for those influential in illicit drugs influencing individual players to "throw" games via the compulsion of blackmail.
He also demonstrates fairly clearly how the NFL has kept buddy buddy with the Feds to keep the Feds out of NFL business as much as possible. It is a very good read, but get the newer updated version if you are going to read it.