What must an athlete wear to compete?

• Shoes: "Athletes may compete either barefoot or in Athletic Shoes on one or both feet."
• Shoe regulations: shoes must comply with the Athletic Shoe Regulations approved by the World Athletics Council. Those are a separate document, which was not read for these pages.
• Clothing: must be "clean, and designed and worn so as not to be objectionable", and made of material that is "non-transparent even if wet".
• The judges' view: athletes "must not wear clothing which could impede the view of the Judges".
• Team kit: at major competitions athletes wear the uniform approved by their federation.
• Bibs: other athletes wear two. "In the Jumping Events ... one bib may be worn on the front of the torso or on the back only."
• As issued: bibs "may not be cut, folded or obscured in any way".
• No bib, no competition: an athlete may not take part without the proper bib or identification.
• Protection: bandages, tape, belts and supports may be worn for protection or for medical reasons.
• The call room: officials there see to it that bibs, shoes and clothing are in order before athletes go out.
• The penalty: an athlete who does not follow these rules and refuses the referee's direction, or competes anyway, is disqualified.
• Hands: gloves are permitted in the pole vault.

A bib on the back can catch the bar or drag in the sand, which is why jumpers are allowed to wear only one. The clothing rules protect the judges' view of the attempt. Shoes are controlled because their soles and spikes can add to a jump, so World Athletics approves what may be worn.