You can legally bet on sports only in a few places in the U.S. And there, you have to have the money up front. Mob bookmaking operations take bets on credit and typically settle up weekly. That's where the loansharks often come in if the bettor doesn't have the money to cover his losses. That's why they're the two main "bread and butter" rackets for the mob. They bring you in with the gambling and keep you with the loans.