What is caps and numbering in Water Polo?

Section 2: Equipment

Men's ball: Circumference 68–71 cm (26.8–28 in), weight 400–450 g (14.1–15.9 oz)
Women's ball: Circumference 65–67 cm (25.6–26.4 in), weight 350–400 g (12.3–14.1 oz)
Waterproof, non-absorbent outer surface with a textured grip coating
Inflated to 90–97 kPa (13–14 psi), must float when released
Typically bright yellow for visibility; contrasting color to cap colors
Ball approved and stamped by World Aquatics for international competition (WP Rule 3)

Each team wears distinctly colored caps: one team wears white, the other dark blue (or contrasting dark color)
Goalkeepers wear red caps, numbered #1 (starting goalkeeper) or #13 (reserve goalkeeper)
Field players numbered 2–13 (excluding 1 and 13 for non-goalkeepers)
Caps fitted with integrated ear guards to protect against impact and facilitate hearing the referee
Caps secured by chin straps; cap must be worn at all times during play
Numbers must be at least 10 cm (3.9 in) high, printed on both sides of the cap

Width: 3 m (9.84 ft) between the inner edges of the goalposts
Crossbar underside: 0.90 m (2.95 ft) above the water surface when water depth is 1.50 m (4.92 ft) or more; 2.40 m (7.87 ft) from the bottom when depth is less than 1.50 m
Goals may be rigid (anchored to the pool deck or wall) or floating (secured to prevent movement)
Net must be attached to the goal frame and extend at least 0.30 m (1 ft) behind the goal line
Goalposts and crossbar painted white; contrasting markings not permitted

Swimwear: Non-transparent, one-piece or two-piece swimsuit (no body suits extending past shoulders or knees)
Mouthguards: Recommended but not mandatory under World Aquatics rules
No jewelry, watches, or hard accessories permitted
Fingernails must be trimmed short; referees inspect before each match
Goalkeepers may wear a face mask at their discretion (no competitive advantage permitted)

Men's ball: Circumference 68–71 cm (26.8–28 in), weight 400–450 g (14.1–15.9 oz)
Women's ball: Circumference 65–67 cm (25.6–26.4 in), weight 350–400 g (12.3–14.1 oz)
Waterproof, non-absorbent outer surface with a textured grip coating
Inflated to 90–97 kPa (13–14 psi), must float when released
Typically bright yellow for visibility; contrasting color to cap colors
Ball approved and stamped by World Aquatics for international competition (WP Rule 3)

Each team wears distinctly colored caps: one team wears white, the other dark blue (or contrasting dark color)
Goalkeepers wear red caps, numbered #1 (starting goalkeeper) or #13 (reserve goalkeeper)
Field players numbered 2–13 (excluding 1 and 13 for non-goalkeepers)
Caps fitted with integrated ear guards to protect against impact and facilitate hearing the referee
Caps secured by chin straps; cap must be worn at all times during play
Numbers must be at least 10 cm (3.9 in) high, printed on both sides of the cap

Width: 3 m (9.84 ft) between the inner edges of the goalposts
Crossbar underside: 0.90 m (2.95 ft) above the water surface when water depth is 1.50 m (4.92 ft) or more; 2.40 m (7.87 ft) from the bottom when depth is less than 1.50 m
Goals may be rigid (anchored to the pool deck or wall) or floating (secured to prevent movement)
Net must be attached to the goal frame and extend at least 0.30 m (1 ft) behind the goal line
Goalposts and crossbar painted white; contrasting markings not permitted

Swimwear: Non-transparent, one-piece or two-piece swimsuit (no body suits extending past shoulders or knees)
Mouthguards: Recommended but not mandatory under World Aquatics rules
No jewelry, watches, or hard accessories permitted
Fingernails must be trimmed short; referees inspect before each match
Goalkeepers may wear a face mask at their discretion (no competitive advantage permitted)