Antipodists are
acrobats or
jugglers who perform their tasks with their
feet, normally lying on their backs.
One variety of the antipodist act is called Icarian games - the antipodist is lying on his back in a special chair, juggling a voltigeur (flyer) with his feet.
The word is, of course, related to "antipodes", stemming from Greek, referring to diametrical opposites or persons dwelling on opposite points of the globe, the "pod" part meaning feet.
According to the essay "A brief history of juggling", antipodism was often found in Aztec art.
Famous antipodists' acts include those of the French troupe Les Castors (http://mouvance.com/castors/) and madman/Frenchman Leo Bassi (http://www.leobassi.com), fourth generation antipodist, who refers to his father as "the world's greatest foot juggler".
Sources:
http://www.circusland.com/favorites/eng/glossary.html (A circus glossary! Brilliant.)
http://reedycreek.azlance.com/~richasi/Cirque/Varekai/act02.htm
http://www.m-w.com
http://www.juggling.org/books/artists/