We are flyball fans here, and Harley was in the starters this year, although Mayhem is "a different kettle of fish"!!
Keep going with the ball to hand scenario, as this is a great for ensuring the ball comes back to you. With Harley I always have a second tennis ball in my hand, so when he comes back, he gets the second ball as a reward.
With Mayhem, she losses interest in the ball very quickly, and has now got fixated on only playing ball with me, so at training session now, everyone else has to play ball with her!! Although her run backs are really fast, its just the bit in the middle that I have to work on.