Flyball sure looks like fun. I'm waiting for one of the training facilities near me to start offering classes. They are working on it now and I can't wait. I'm sure yous will have a lot of fun.
You would want to take him to some sort of flyball class even if you are doing it just for fun though. The dog needs to be in certain positions when they hit the box to retrieve the ball in order to prevent injuries to their joints & the such.

Please keep us posted on the flyball and good luck!