Fighting between a male and a female happens much less than dogs of the same sex. Were they hackling and showing teeth? In my opinion, dogs that are really fighting would draw blood in an instant, and real fighting normally happens from the start not from play. That does not mean that two dogs cannot get so worked up that they go at each other a bit, but that normally is not a "real" fight. With all this said, I do not allow roughhousing of this type in the house, and very little outside. Without seeing the altercation, it is hard to know what the issue is. I would supervise the interaction for the time being, and stay on them so they understand that you will not allow this behavior. Stopping it before it starts is best, but you will need to learn all about canine behavior, dominance, and posturing in order to do so if you have not already.