Chris and Christian - Thank you for your comments on my last post. They'll definitely help me in crafting future posts here and hopefully providing some more information regarding sports and social networking.
I put together this quick video to roughly outline how sites are engaging and attracting fans. The first two points are pretty basic, but it's important not to overlook them---a site that looks awesome will still fail to become popular if it is not easy to use and has the basic features that people are looking for in a social network.
As for the specific examples about what sites are doing to engage fans...you'll have to watch the video :)
In the future I'll do a better job with these video posts, so it doesn't sound like I'm rambling so much. And I'll try to keep them focused to just one thing/idea to keep them short and sweet. Also there's a bit of lag in the video...thanks YouTube...