Well you have to have a Yahoo ID in order to get into the yahoo games but thats as easy as signing up. Its quick and no cost or anything and plus there's so many yahoo functions i find the ID pretty useful (yahoo launchcast, yahoo games, yahoo fantasy football leagues....)
Its just http://games.yahoo.com/
On the right hand side you'll see a section labelled "Arcade and Other Games" and inside that section is a link for "Trivia"
But you can't get into it unless you've signed in first with your yahoo ID. Inside the "Trivia" section there's a "Football Trivia"