I played girls' hockey at my mixed school, in sex-segregated Games lessons. The boys simultaneously had their Games lessons on the other pitch, rugby and football. One day, towards the end of the spring in Year 11, there were very few people around for some reason (perhaps a trip that not everyone was involved in?) and the PE teachers decided to put the boys and girls lessons together.
In their wisdom, they decided to have us play mixed hockey. Never mind that the girls had been playing for five years and the boys had never had a hockey lesson, so were unlikely to know the rules, they simply equipped everyone with hockey sticks and let us have at it.
I think they mixed the teams, but it was still a disaster. The boys were faster, taller, stronger and tackled far more aggressively than the girls. One boy actually broke a hockey stick while tackling. The game didn't last all that long ( I think the PE teachers at least had the sense to blow the whistle early) but I remember it being pretty terrifying and I am still amazed that no one was injured.
I have never, ever doubted the physical differences between the average man and the average woman.