It seems that Yoshinobu was as strong-willed as his father, Michinaga and, when he was 15 years old, he caused a fight with FUJIWARA no Korenari (the second son of late FUJIWARA no Yoshichika) who happened to be sitting with Yoshinobu in a ceremony celebrating the birth of the Emperor Gosuzaku (later, the Emperor Gosuzaku) and Korenari, who was one-sidedly injured by followers of Yoshinobu who sided with Yoshinobu got angry and became a priest.
父・道長に似て勝気な性格だったらしく、15歳の時に後朱雀天皇（後の後朱雀天皇）誕生を祝う儀式中に同席した藤原伊成（故藤原義懐の次男）と喧嘩をした挙句、加勢した能信の従者によって一方的に負傷した伊成が憤慨して出家するという事件を起こしている。