The neighbor told us of the claw marks in the concrete and fur left from the fight. I did not see how the dog got involved--- my mother saw the aftermath of our cat riding the dog up the street like a bronco buster standing in his stirrups!
Apparently our cat rode the dog much like a jockey rides a horse at the Preakness, ass high, shoulders low, ears back.
The dog was running fast as he could up the street yelping, my guess is that the dog was looking for a fight and this cat was the wrong cat to take it too. I only saw that cat lose one fight in his life and that was when he was 15, and at that, he and another cat rolled off a wall together fighting and the other cat landed on top with my cat hitting the ground on his back, otherwise, who knows, he might have beaten him.