No, not me - the cat! One of our cats really enjoyed playing with hacky sacks but the one I had was filled with sand and I didn't want the sand leaking out all over the house so I made him a replacement that I filled with rice. First I crocheted a very colorful one out of fingering weight cotton and it was such a hit that it wore out. The first replacement was the one on the left made out of worsted weight acrylic. You think he will have anything to do with that one? Of course not. He will run after it but won't pick it up and carry it back to me (yes, my cat plays fetch).
I do not recommend using wool for this project. Do you want your cat to develop a taste for your wool yarn??
First off, I crocheted a circle, increasing as I went until it was around 1 1/2" to 2" in diameter, then a worked several rows without increasing. I decreased over the next two rows and stopped here to fill the sack. To keep the rice from working its way out through the holes in the crochet I used the toe of an old sock from the rag bag (does anyone else still have rag bags?) and added rice one tablespoon at a time and test fitting it in the bag. Don't fill it very tight because I found that the cat preferred the bag to droop and sag a bit - probably feels more like a dead mouse. Once you have added the right amount of rice for your bag, sew the top of the sock closed and cut off the excess. Put this bag inside your crocheted shell and continue working around, decreasing as you go until the ball is complete and the opening is small enough to sew shut.