When the retired Emperor Gotoba raised an army to overthrow the Shogunate, which is called Jokyu War in 1221, Kanetsugu, 14 years old then, followed his grandfather Shigetada YAMADA and his father Shigetsugu to fight for the retired Emperor.
承久3年（1221年）に後鳥羽上皇が倒幕の兵を挙げると（承久の乱）、当時14歳であった兼継も祖父・山田重忠、父・重継に従い上皇方として戦った。