This paper describes Squidball, a new large-scale motion capture based game. It was tested on up to 4000 player audiences last summer at SIGGRAPH 2004. It required the construction of the world’s largest motion capture space at the time, and many other challenges in technology, production, game play, and study of group behavior. Our aim was to entertain the SIGGRAPH Electronic Theater audience with a cooperative and energetic game that is played by the entire audience together, controlling real-time graphics and audio by bouncing and batting multiple large helium-filled balloons across the entire theater space. We detail in this paper the lessons learned.