Some of the most entertaining things about sports are what the fans do. From signs to chants, fans and their interactions with players, coaches, and referees add a great deal to the experience in the stadium and even on television
While this can be true of fans that run onto the fields (video compilation of the best here: Best Of Fans Running Onto Field), there are potential dangers. For one thing, fans themselves get hurt by being tased or subdued by security gaurds. There also has to be concern for the people on the field as well as bomb threats and other sorts of terrible acts.
While the video below is good hearted in that no damage is done, this is not something that I hope becomes a trend.