Wikipedia
Pasola is a game played by the Western Sumbanese to celebrate the rice planting season.
The game is played by throwing wooden spears to the opponent while riding a horse. The game is played by two different groups of men from different clans or tribes. It is a game that requires a high skill at horse riding and spear throwing skill.
It ends up in a bloody game when the wooden spear hit the bare flesh of the participant. In the Sumbanese ancient beliefs, the spilled blood will fertilize the land and multiply the output of the paddy. Religiously speaking, the ritual battle of Pasola, is "essentially a fertility rite. Like the cock-fight, it is designed to shed blood on the earth" Likewise the people of Sumba, within their religious traditions are "believers of the spirits of nature and their ancestors" as are the people of Nias and the Toraja of Sulawesi.
In the Wanukaka region, as part of the ritual, early in the morning the marapu priests and their entourage go the beach to perform a prayer. They sacrifice a black cock to the gods and check the heart of the cock to read the signs from the gods on whether to proceed with the pasola as they attempt to gain the answer to their question by this ritual of divination.
They descend to the sea afterwards to collect the colorful sea worm as part of the ritual, then proceed to the area where the game will be played.