I built a site to run tennis leagues. We have started in the bay area with 210+ matches taken place since February when it launched. Most other sites that try to do this look like they are built in the 90s and have little support for modern features like communicating via Whatsapp or decent mobile support. It could also be extended to other (racket) sports later. People pay a $20 fee for each league, which is about 8 matches in 8 to 10 weeks. http://www.racketlogger.com

The goal is to scale it across the US (and beyond, to any english-speaking area). Doing cost-effective marketing is key. How do we get the word out? How do we improve the site and experience so much that players tell their friends?

We put effort in SEO building a large database (the largest?) of string and racket specs with the goal of attracting some of the core fans of the sport (we started to get some clicks a day). There are a ton of other "social" and related ideas, the question is how to select which one(s) will work best.