I had a male and female for years, and they did get into a fight. I always felt like the female was the instigator. She was a pretty nasty animal, and she would always seem grumpy toward my male lab (neutered). One day she was sniping at him and he really went after her. It was terrifying. My guess was that he had just had enough of her attitude through the years and snapped. He never did it after that, and they got along fine. She was nicer for a few days, then went back to her normal grumpy self.