And if you don't know what a haka is, you can find out by clicking here or watching a proper one here (if you are impatient, the second link is best).
But it's basically a traditional dance originated with the native New Zealanders (Maoris) and has been adopted by their ruby teams since as an intimidating ritual performed before the other team each game, most popularly by the All Blacks.
Now that the [brief] history lesson is over, this video should make some sense.
I couldn't help not posting this.
I get a kick out of it every. time.
I think it's safe to say jockeys are one of the least intimidating athletes out there. In fact, i'm sure it's why Toby Maguire made such a good one.