For those of you who are unfamiliar with Theatre Sports it involves teams of 4 or 5 people performing a number of unscripted comedic tasks, often involving audience suggestions.
An example is Guess My Word where an improviser leaves the theatre to allow the audience to suggest a secret word. The improviser then returns to the theatre and tries to guess the word as suggested by another improviser in a scene.
It's real seat-of-the-pants stuff, requires raw comedic talent and timing, and if done well is hilarious. It goes without saying the the national champs should be quite a show.