The fish digs a shallow crater in sand or rubble, deposits eggs in it, and guards them. The defended space is not a sphere around the nest. It is a cone with the apex at the nest and the opening at the surface, because the fish's concern is anything above its eggs, and the higher an intruder is the wider the area it could be threatening from.
The practical consequence is counter-intuitive. A diver ascending to get away stays inside the cone and can remain inside it for a long swim upward. Withdrawing horizontally along the seabed, keeping fins toward the fish, leaves the territory much faster. Dive briefings across the Indo-Pacific give this advice and it follows directly from the geometry.
Bites are real. The jaws are built to crush sea urchin tests and can cut through a wetsuit and into a finger or foot. Attacks are territorial rather than predatory and outside the nesting period the same fish will usually retreat. The species also carries a ciguatera risk in some regions, so it is not reliably safe to eat.