The game is typically played on sand, which makes it easier to dive head-first when striking the ball. The game is like a netless tennis or volleyball game where each team strikes the ball (made of tree sap) over a central division line. A team earns a point when the ball cannot be returned, or a player touches the ball with something other than the head.
This game resembles a version of net-less volleyball and tennis. However, players can only make contact with the yoga ball with their heads!
The playing area is rectangular with a middle division line.

Source: https://www.montessoriphysicaleducation.com/new-blog/xikunahati-traditional-indigenous-sport-of-brazil2023/1/13

When a player strikes the ball with their head, they must sprint to one of the extra players and switch with them. This gives everyone turns to play.

Source: https://www.montessoriphysicaleducation.com/new-blog/xikunahati-traditional-indigenous-sport-of-brazil2023/1/13

The game begins by having one player “serve” the ball to their opponent by bouncing the ball to their opponent. Like volleyball, the team that scored last is the team that serves.
Players can strike the ball with only their heads.
If the ball bounces, they might head it like soccer. Some of the smaller players can bend down to hit the ball successfully if the ball is rolling. However, to create the best hit (which may be required for taller players), one should dive toward the ball, strike it with their head, and catch themselves afterward.
An important note for the players is that they should “call” for the ball. They might collide heads. Limiting the number of players on the court helps prevent those accidents. However, players still need to communicate with each other.
The other team receives a point if the ball touches anything other than the head first.
A team gets the point if they hit the ball and it crosses the other team's boundary line.
A player can only touch the ball once in a row. If a player touches the ball twice in a row, that is a point for the other team. This shouldn't happen if they quickly substitute after hitting the ball. However, a strategy from the other team is to return the ball immediately to the person who just hit the ball, which would cause a double hit.