With the start of the NFL season, football fans are measuring player performance and building virtual rosters for seasonlong fantasy sports leagues. These commissioner-style games, in which players create fantasy “teams” with a roster of real-life athletes that “play” over the course of the sport’s regular season, are offered on big platforms such as ESPN.com, Yahoo.com and CBSSports.com. While none of these companies have detailed fantasy revenue or user totals, there is no doubt these …