Your best bet is to run a browser in a virtual machine, preferably Linux or a flavor of BSD- don't use Adobe's security disaster known as flash, use chrome to handle it instead. Once the game is over, roll back the VM to its previous saved state. Store no passwords or identifying information on the VM or via google and chrome.
If that's too much to handle technically, try downloading a pre-rolled appliance for Oracle's VirtualBox or VMWare's VMPlayer- both products are free and have browsing appliances for just this sort of use case.
P.S. Don't bother with any sites that advertise "American Football Matches"