The sports landscape is littered with failed professional football leagues, such is the dominance of the N.F.L.
Yet the sports agent Don Yee, who represents New England Patriots quarterback Tom Brady, thinks he may have found a model that will work: a league for 18- to 21-year-old players who skip college to play professionally right away.
Most fledgling leagues, like the defunct U.F.L. or the X.F.L., had rosters filled with castoff players who had gone undrafted out of college or who had bounced around pro teams. The quality of play was uneven, while games often overlapped with the N.