I don't know what my Lab would do in all honesty, as when we are out he just loves it when anyone greets him, so I think he just trusts everyone tbh.
My other x breed, I reckon she would put herself between us and appear aggressive. She isn't at all but she has that presence about her which seems intimidating.
Many years ago my ds who was around 8 at the time was walking out old Lab. He would just plod along as he was old and arthritic. Out of nowhere a Rottweiler which had got loose ran over and went for my ds. My Lab threw himself on top of my ds and the Rottweiler mauled my Lab in his back end. I was actually out and my exdh was home and this happened around the corner from our house. Ex heard the screams and everyone came running out of their homes and one older lady beat the Rottweiler away with a broom. It was a horrific attack. The owners were not home and had left their gate slightly open. My ds was so badly traumatized and my Lab spent a week admitted with his injuries with drains etc. I made contact with the owner, and to put it mildy, he could not have given a shiny shit. I asked him to pay the vet bills and at was a struggle. Eventually he through an envelope of cash into my garden. He couldn't even face me. They moved shortly after. I reported them and the dog, actually the vet did as well but nothing came of it.
I know that my Lab saved my ds's life as if he had been bitten as much as DDog did, he woukd not have recovered as well (he was a tiny 8 year old).
We lost DDog about 18 months after this, we kept his ashes and we chat to him all the time, he was a very special boy.
My ds is in his 20s now and will not walk that same route with any of the dogs.