of concussions and outside England also has the highest number of catastrophic injuries out of any team sport. Research finding that during match play, concussion was reported at a higher level, and during training at a lower level, but still at a higher level than most players of another sport to receive. Rugby ball A rugby ball is a diamond shape ball used for easier passing. Richard Lindon and Bernardo Solano started making balls for Rugby school out of hand stitched, four-panel, leather casings and pigs' bladders. The rugby ball's distinctive shape is supposedly due to the pig's bladder, although early balls were more plum-shaped than oval. The balls varied in size in the beginning depending upon how large the pig's bladder was. In rugby union, World Rugby regulates the size and shape of the ball under Law 2 (also known as Law E.R.B); an official rugby union ball is oval and made of four panels, has a length in-line of 280–300 millimetres, a circumference (end to end) of 740–770 millimetres, and a circumference (in width) of 580–620 millimetres. It is made of leather or suitable synthetic material and may be treated to make it water resistant and easier to grip. The rugby ball may not weigh more than 460 grams or less than 410 and has an air pressure of 65.71–68.75 kilopascals, or 0.67–0.70 kilograms per square centimetre, or 9.5–10.0 lbs per square inch. Spare balls are allowed under the condition that players or teams do not seek an advantage by changing the ball. Smaller sized balls may also be used in games between younger players. Much larger versions of traditional balls are also available for purchase, but these are mainly for their novelty attraction. World Cups The Rugby League World Cup was the first World Cup of either of the Rugby codes and was first held in France in 1954, and as of 2013 occurs on a 4-year cycle. It is an international tournament that is organized by the Rugby League International Federation. The event is played in the league format and features the top 16 teams from around the world. Australia won the 2017 Rugby League World Cup, played in Australia, New Zealand and Papua New Guinea. The Kangaroos backed this up by winning the 2021 tournament also. The Rugby World Cup, which was first held in New Zealand and Australia in 1987, occurs every four years.