As a sports fan, I love that athletes are active in social media. Take a look at ESPN and TSN. They have fully integrated into social media by having their sports analysts consistently report breaking news on Twitter and Facebook. Even though athletes are permitted by contract to participate in social activities, there are still a number of rules they have to abide to. Never the less, I think the NBA, NFL, MLB, FIFA, MLS and the NHL have seen the importance of social media and how it helps athletes engage with their fans.
Take a look at this infographic and see how social media has impacted sports.