Purchase tickets and join the fans at a game at Mong Kok Stadium. If there's nothing happening while you're in town, you might like to check if they give a guided tour of the facilities.
Situated in Mong Kok, this sporting facility is worth a look. But you'll find loads more to see in this area. Lan Kwai Fong, Harbour City, and Nathan Road Shopping District are within close reach of Mong Kok Stadium.