The puppy is 10 weeks old. It had lived in the foster home for 2 weeks with a mellow 5 year old neutered Golden Retriever. It was returned because it was terrorizing the retriever and the wife of my friend. Hard puppies usually have strong prey drive. This is the drive to chase and bite.
Prey drive is a genetically inherited drive, as is hardness.
They do not necessarily go hand in hand. There are a million dogs out there with a ton of prey drive that are also very soft dogs. So don't confuse this issue. I have not seen hardness in pups that do not have a strong prey drive. If hard pups don't have something to chase they will find something to bite.