How would you play soccer in space? basketball? ping pong? Definitely you'd want to use soft balls so you wouldn't harm your equipment.
There is a wonderful DVD from the Houston Museum of Natural Science called "Toys in Space". On the ISS they took several international sports and tried to see how well they would work in zero-G. You can order the DVD from
http://www.spaceupdate.com/?order.html
(scroll down to the bottom of the products).