Well, it's called moa in Tongan, and I bet it's not what you think. It's a form of....jacks! I don't see it being played on the playground too often, but I started asking some form 1 girls about the game and they obliged with showing me all the different levels and rounds. I love seeing games (like Tongan checkers) that have a connection to games we know.
Moa is played with 5 small stones, all about the same size. The way you throw them and catch them makes the game. Like jacks, it starts out easy and the moves get progressively more difficult. They begin by throwing up a stone and picking up another and catching the stone they threw. Then it's 2, etc. The last rounds are really tricky as they catch the stones on the back of the hand and have to let one drop between the fingers, the next time 2, etc. They're really fast and good at it, so I had to ask them to show me several times. Great fun! Here's the way the rounds were told to me:
Hapohapo (like juggling)
Fetongitongi (changing rock)
Tupe (throwing up the rocks and landing on the back of the hand)
Puaka (fingers get stretched out. With the rocks on the backs of the hand they are dropped between fingers.) Puaka, by the way, means pig.
Maybe a few photos will help: