Although MINAMOTO no Yoritomo, who was a bereaved child of Yoshitomo banished to Sado, raised his army against the Taira clan, he was defeated by Kagechika OBA and other commanders on the Taira side in the Battle of Ishibashiyama in August, 1180, and forced to run to the Boso peninsula, hiding himself in the residence of Tsunetane CHIBA, who declared to support Yoritomo.
治承4年（1180年）8月(旧暦)、伊豆国に流されていた義朝の遺児・源頼朝が打倒平氏の兵を上げ、石橋山の戦いにおいて平氏方の大庭景親らに敗れて房総に逃れると、頼朝への加勢を表明した千葉常胤の館に入る。