June 22 (Reuters) - Focus on judo at the 2020 Tokyo Olympics: THE ABSOLUTE BASICS * Men and women compete in seven weight categories, ranging from under 60kg to over 100kg for men, and under 48kg to over 78kg for women. * Judo, meaning "gentle way", involves throwing or taking down an opponent, subduing them with a hold or forcing them to submit with a joint lock or a choke. * Athletes face off on 10m x 10m tatami mats and deploy any of 100 techniques comprised of 68 nagewaza (throwing) and 32 katamewaza (holding). * An athlete scoring "Ippon" -- which can be achieved via a throw, a submission or holding down an opponent for 30 seconds, wins the bout straight away. * If the bout goes the full four minutes, the winner is decided on the number of points accumulated. HOW MANY MEDALS? There are 15 gold medal events at Tokyo, including 14 individual and one team. WHAT HAPPENED IN RIO? Japan won three gold medals, followed by two each by France and Russia. A total of 126 nations competed in judo, with 26 winning medals. Among the gold medalists, France"s Teddy Riner defended his title in the men"s +100kg WHAT CAN WE EXPECT IN TOKYO? Riner will aim for his third consecutive Olympic gold, which would match the record held by Japan"s Tadahiro Nomura. WHAT"S NEW? A mixed-team event will be introduced, involving teams of three male and three female judokas. The International Judo Federation (IJF) revised rules in 2016 to shorten men"s bouts by a minute to make them more exciting. Bouts now last four minutes for men and women. WHEN IS IT HAPPENING? July 24 to 31 WHERE IS IT HAPPENING? Nippon Budokan, in the Chiyoda-ku ward of Tokyo, originally built for the Tokyo 1964 Games. HOW DID WE GET HERE? Judo originated in Japan in the late 19th century and was introduced to the Olympics at the 1964 Tokyo Games, though only men were allowed to compete. A women"s competition was brought in from Barcelona 1992. WELL FANCY THAT Judo became the model for other modern Japanese martial arts and gave rise to a number of derivative martial arts around the world. It also influenced other combat styles such as shoot and submission wrestling.