i am not sure (which i know isn't a helpful answer. I used to run a flyball group and we had insurance for that, but i think that was because we used to "make" money from it (not really make - we used to charge £2 per session and use that money to buy equipment)
One time a lady fell over a bit of equipment at the group and broke her leg and as she was self employed, she did discuss suing us to cover her losses. She never did sue us, but i sure would have been glad of the insurance if she had've done. the insurance itself wasnt too expensive - it was about £70 PY and covered us for dogs biting people, causing accidents etc as well