What will happen to your league when the founding members are all too arthritic to catch a football, or adult kickball loses its hipster appeal? How will you recruit and train new volunteers and keep young players coming in to replace those lost to busy careers, family responsibilities or the decidedly un-fun physical surprises that come with middle age?
Consider forming youth teams to build interest among the school-age set, or even a "silver league" for those who'd like to play shorter halves -- or at a slower pace. If your league has a revenue surplus in its peak years, set aside a rainy day fund for rebuilding and maintenance expenses that you might encounter down the road. And don't forget to set up a succession plan to pass your knowledge and enthusiasm to the next generation in the unlikely event that you ever decide to hang up your cleats.