I know how this feels. sorry you and the pup had to go through it. I took my dog for a walk ( staffie ) and went into a field. He was on his harness with lead and a collar. A Alsation came over and started to sniff him my dog stood completely still when the other dog started trying to bite him. i swang my dog with the lead out of the way of his attacks but he grabbed hold of my dogs leg.
I dropped my dog to the floor and scrabbled for the Alsations collar and guess what, nothing there. Last resort was to grab the dog in a head lock until the dogs owner came over and dived on him… I hurled abuse at him for him not having a collar on his dog as its easy to control them with the collar as you can twist it to cut there air supply.
truly awful also got chased by a Alsation on my mtb the guy shouted ” Oiiii stop he dont like bikes”. Surely the idiot should have him on a lead in a public park then?