The Haka is a traditional Maori challenge before battle, and is performed before every match played by the New Zealand national rugby team, known by the name The All Blacks. The All Blacks are the most feared and respected rugby players in the world.
The Black Ferns are New Zealand's National women's rugby side, and are the current Women's Rugby World Cup Champions (played in Canada, this summer).
I tried to get some video (with sound) of the Black Ferns distinctive Haka, but I couldn't, so here is the video sans sound.
The women's haka isn't an invitation to combat, rather it is a ritual of their togetherness as a team.
In either event, as a rugby player (not that I am, mind you), I would be intimidated by either of these groups.