For most of us, the athletes are what make sports interesting. But if you own the team or run the league, your players are essentially very expensive migrant workers who eat into your profits. We talk to N.F.L., N.B.A., and U.F.C. executives about labor costs, viewership numbers, legalized gambling, and the rise of e-sports. (Ep. 5 of “The Hidden Side of Sports” series.)