There's a sports stock market exchange called StarStreet. It's pretty new. It uses real money and you invest in athletes and then sell them anytime you want. You don't have to change your roster every week but you'd probably be smart to sell if one of your guys goes on injured reserve. ThePit.com is less of a pure stock exchange as you invest in rookie cards of the players but still worth a shot (for basketball Kevin Durant went up 600% there in a year).