Which sport uses the biggest ball?

The extreme sport of Zorbing !

Calling all Zorbonauts! Have you been to planet Zorb?
If you haven't heard of Zorbing, it is a brand new extreme adventure ride that is typical of the innovative and exciting thrill-seeking activities that all seem to originate in New Zealand.

Zorbonauts are flung downhill while strapped inside an enormous air-cushioned bouncing ball. Zorbonauts say %91goodbye' to gravity and experience the magic of weightlessness that only they and space-travellers can experience.

The Zorb itself is a gigantic inflatable pvc ball standing about three metres in height.
http://www.zorbingtime.com/zorbing/

The hippies came up with a sport called EARTH BALL - Where a crowd of people together would push at a HUGE rubber ball (the size of a small house) at the same time. This caused the huge ball to move and bounce. There was no winner in this game but it was lots of fun for all involved.