A widely accepted theory is that with both Tsunefusa and his elder brother assuming the post of Governor of Izu Province, he had relations with Tokimasa HOJO, who was the foster father of Yoritomo and a local officer in the Izu Province government, and using this connection, communicated with Yoritomo secretly from around the time when Yoritomo started raisnig an army.
有力説とされているのは、経房は兄とともに2代にわたって伊豆守の地位にあったことから、頼朝の義父で伊豆国の在庁官人であった北条時政との関係があり、その縁で挙兵前後から秘かに頼朝と連絡を取り合っていたという説である。