Select wool and pattern, I I used the African football pattern, see link above, and @ladycassandra84 used a spiralling method.
For the flower football yoga ball, I followed the pattern in the above link, however in order to make it big enough to fit the ball after each flower is formed I did two rounds of double crochet followed by two rounds of triple crochet.
Cassandra's stripey Amazeball was made by crocheting a spiral and then trying it around the ball and increasing as necessary, for more information please contact @ladycassandra84 on twitter for more info
Leave a hole so the ball can be re inflated as necessary.
Enjoy your Amazeball, if you make one please show us, we would love to see It!!