I never actually had them yield by sheating my own weapon, but the runners/screamers who get into fetal position is quite common. Just happened to me a few minutes ago in fact, amusing enough it was the Bandit Chief. It was at Robber's Gorge, I had finished off all his guys and ran to the main shack where he stormed towards me. I expected I huge fight, but after two hits which barely caused any damage he just ran off. I jumped up on some rocks and saw him crouching down further down the road. Not knowing the added lines given by sheating, I left him alone.
One time it happened before I had even attacked anyone, I just ran towards the cave and he went into fetal position as on commando, maybe he was a left over from my last raid? Anyhow, he knew how badass I was, kudos to him. Killed him anyways though (wanted his arrows and other potential loot) but I did feel slightly sorry about it.