Kellar, an English Springer spaniel, was born blind. He can’t see the ball, but he can find it and bring it back! He plays fetch completely by ear. Kellar can hear (or feel) the ball hit the ground, and then it's a matter of following directions. From the YouTube page:
Kellar was originally trained to play ball with the commands "hot" and "cold". We later added "warmer", "passed it", "left" and "right". The process took about a week for the basic commands.