Kellar, an English Springer spaniel, was born blind. 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.