Extracts from the C.M.A.S. International Rules for Underwater Hockey (p2, 4th edition, 1990)

2.2 Team Personal Equipment.

• 2.2.1 Each player shall be equipped with a mask, which must have safety glass or other safety material fitted; a non-metal, pliable snorkel (if desired); a pair of conventional underwater hockey fins (made of rubber or other non-dangerous pliable synthetic material, excluding fiberglass) which are approved by the C.M.A.S. Underwater Hockey Sub-Committee; and an underwater hockey stick.
• 2.2.2 A protective glove may be worn on the playing hand if required, provided it does not contain rigid or sharp reinforcing material.
• 2.2.3 Head caps with firm polyethylene or rubber ear protector(s) must be worn.
• 2.2.4 Protective knee and/or elbow pad(s) may be worn if required, provided they are constructed of soft materials.
• 2.2.5 Wet-suits and/or weight belts may not be worn.
• 2.2.6 All personal and team equipment must have the prior approval of the Chief Referee.

These rules still apply for both local club and schools' leagues, but some concession is made for school teams with regards to hats. School players are not (currently) required to wear protective hats for the local league, although it is strongly recommended. It is a requirement however that hats are worn at Schools' Nationals.