Oh, that looks painful. It may look like a belly-flop contest, but this Norwegian sport is called dødsing. The video was taken at an event at Frognerbadet in Oslo this past Saturday. Redditor aMagnu explains how it’s done.
It's not a bellyflop competition, it's called dødsing which kinda translates do "deathing". The idea is that you spread out as you would for a bellyflop, but tuck into a sort of folded-in-half-dive right before hitting the water. The contestants are scored based on style and how long they wait before tucking in. I'm pretty sure a full-blown bellyflop from that height (10m) is potentially very harmfull. As the name implies it's about narrowly avoiding death.
Phunkstar, who is actually in the video, explains the history of dødsing.
Well, there's a context where this is natural, let me just say that up front. In the end of the 60's / beginning of the 70's, Oslo youth would hang out at the pool where this diving tower is, and the "rebels" would dare each other to do døds to impress the girls, but also to be a counter culture to the more established and more elegant traditional divers. Diving has strict rules and has to be elegant, and Oslo is a divided city in many ways. Working class on the east side, posh people from the west side. Diving was a classical west side activity, along with tennis and golf, and so dødsing was a massive middle finger from the east side boys to show that they could do daring stuff as well, and much cooler. Along the coast of Norway there are also a lot of cliffs that are perfect for jumping so dødsing has spread out of Oslo all over the place and is a typical summer activity for many who are into this sort of thing. Another thing to note is that other there are other diving towers with 10m platforms close by Oslo, and they are not regulated, so there are no rules. People do shit like this because it is fun, and to impress their mates and girls basically.