The sign besides the rock tells the following story:

Maui's stone throw
This massive stone in Tongan legends recounts the story of demi-god Maui Kisikisi, who was angrily awoken by the crowing of his father's rooster that he tried to kill it. The frightened fowl escaped from ʻEua to Tongatapu but Maui Kisiksi kept hurling rocks at it, where by this boulder, which is the largest would be the one that slaughtered the rooster.
Tsunami rock
Researchers hypothesize that this large coral boulder, which is believed to be the largest tsunami rock in the world, was brought 100m inland from the surrounding reefs by a massive tsunami that hit Tonga approximately thousands of years ago.

FOKI