Yamashita qualified for the Olympics for the first time in 1976 as a replacement during his freshman year at Tōkai University. At age 19, he became the youngest judoka in history to win the open category of the All-Japan Judo Championships in 1977. He continued his success by winning a gold medal at the 1979 World Judo Championships, and secured a spot on the Japanese Olympic team in a highly publicized draw against 1976 Summer Olympics bronze medalist Sumio Endo. Yamashita went into the final of the 1980 All Japan championships as the favorite, but Endo put Yamashita in a Kani Basami, breaking Yamashita's fibula. The match was declared a draw even though Yamashita was hurt and unable to continue. Kani Basami had been a legal move until the match, but the seriousness of Yamashita's injury caused officials to prohibit its use in international competitions.