A school's "sports day" is called 運動会 (undoukai) in Japanese.
The Japanese word for "sport" is supootsu, pronounced "soo-poh-tissoo".
Traditional Japanese sports include:SumoKendoAikidoJudoKarateKyudo
A popular sport is either baseball or football.
sumo
archery.
Japanese baseball
I think snowboarding is an American sports, I mean it was known in as foreign sport and American where known doing snowboarding than Japanese.
The Japanese use a bamboo sword in a sport called "kendo".
Sumo is a Japanese sport. There are Chinese sumo wrestlers.
The most common sport in Japan is football or soccer, although many Japanese people practice the Martial Arts. However, there is no legally official sport of Japan but the Japanese Sumo Association quotes it the national sport.
I think sumo is the answer you are looking for.
It varies from sport to sport and day to day.