What happens when a water polo player is hurt or bleeding?

• Bleeding: "the referee shall immediately order the player out of the water with the immediate entry of a substitute and the game shall continue without interruption".
• Coming back: once the bleeding has stopped, the player may return as a substitute in the ordinary way.
• Other injuries: the referee "may briefly suspend the game ordering the immediate substitution of the injured player, if needed".
• The restart: the team that had the ball when play stopped puts it into play at the place of the stoppage.
• Leaving the water: allowed during play only with a referee's permission or for accident, injury or illness.
• Returning: a player who left legitimately re-enters from the team's re-entry area at a suitable stoppage, with a referee's permission.
• Entering from anywhere: a substitute for a bleeding or injured player may enter from any place.
• Before a penalty throw: injury and bleeding are the exceptions to the ban on substitutions.

The glossary has substitution and the exclusion re-entry area.

Blood in shared water is a risk to everyone in it, so the player goes at once and the team is not made to play short. The regulations say outright that "Water Polo is a contact sport" with the highest rate of traumatic injury among the aquatic sports, and they require the medical team to be ready for cuts.