The Haka is a traditional Maori dance and "war cry" - although it's not solely about war. Because many of the early New Zealand rugby teams had a very high proportion of Maoris, they incorporated their own cultural twist. A dance that is meant to draw on the strength of the spirits of their ancestors while reaching for the sun - a symbol for the ultimate prize, victory and immortality.
Many other South Pacific / Polynesian cultures have similar, yet different variations of this dance, as was shown in the video with the Tongan team.
Personally, I think it's tremendous and I'd love it if our national lacrosse or even hockey team had a variation based on our First Nations' traditional ceremonies. It pays homage to the past and is a great way of honouring cultures that came before us - the people whose land we now possess.