ANY dog who loves you will come to your defense.
My little 45 pound Chocolate Lab is a fully trained obedience, agility, and retrieving dog with a wall full of ribbons and titles. Sweet as pie, loves people, but takes no guff off anybody (including the black pup). Anyone who looks like they might intend me harm finds a little demon in their path.
We were out walking and met a loose pit bull who started stalking us. She turned, got between the dog and me, lowered her head, lifted all her hackles, and just rumbled at the dog, way down in her chest. He decided that he just didn't want to face a crazy Lab, and turned around and left.
On the other hand, we met a fellow with a half full bottle of whisky and a pit bull puppy named Trouble . . . . but he was at the happy drunk stage, and Trouble approached my girls very humbly, tail down and puppy bowing. They are now the best of friends and there is much kissing and tail wagging when we meet.
Between the humans? or the dogs? :-)