Don't spend too much time talking about first. I would show them some of these videos:
http://www.youtube.com/watch?v=Ex90Aw4PdAI
http://www.youtube.com/user/FIRSTWor.../3/biOfnBxuW84
This is my favorite video so far.Tell them this is the field where the Atlanta Falcons play.
http://www.youtube.com/user/FIRSTWor.../3/f8SDJTUTKUE
Also, show them some TBA videos of awesome matches. Any one with 469 would be perfect to show how the game can be manipulated extremely well!
I hope some of these help. With a custom video that we made last year, we received 15 new kids this year (on a team of around 35). We believe that the video was a big contributing factor. We showed it at the middle school to all of the 8th graders that would be in the high school the next year.