A Water polo cap is a piece of headgear used in water polo.
The caps are used to protect the ears from injury possibly caused by a water polo ball hitting the ears at high speed. They are also used to identify the player, using the number on the cap.
Caps are differentiated by the number printed on them as well as the color. Players from the visiting team will wear light colored caps, whereas the home team players will wear dark caps.
The goalkeepers wear quartered red caps, numbered "1", while substitute goalies have caps which are either numbered "1-A" in NCAA games, or "13" in FINA international games.
In underwater hockey, water polo caps are worn by competitors to help make the teams distinct from each other, and to offer some protection to individuals against the possibility of a burst eardrum caused by the blade of a swimfin making direct contact across the ear. Opposing teams wear either light or dark caps, whilst the water referees wear red caps as well as bright (often yellow) shirts and orange gloves.