Lifespan: Unknown to Eiroku 3 (1560) (?)
Title: Assistant Captain of the Bureau of Cavalry of the Left Division
Lord: Oda Nobuhide → Imagawa Yoshimoto
Father: Yamaguchi Norifusa
Yamaguchi Noritsugu served as a bushō during the Sengoku period. He was a retainer of the Imagawa clan and served as the lord of Narumi Castle in Owari Province.
The Yamaguchi clan were members of the Ōuchi clan of Suō Province. Noritsugu was born as the son of Yamaguchi Norifusa, the lord of Sakuranakamura Castle in Owari.
He is surmised to have been a dogō, or landowner, in the environs of Kasadera in Owari. In a letter dated 12/20 of Eishō 6 (1510), he gave donations to the Ryūfuku Temple in Kasadera. In support of Oda Nobuhide, Noritsugu served with valor in the Battle of Azukizaka against the forces of Imagawa Yoshimoto, a sengoku daimyō with control over Suruga, Tōtōmi, and Mikawa provinces. Although the chronology is unclear, he served as a mediator between Nobuhide and Yoshimoto, achieving a temporary peace between the two sides.
Noritsugu served in important roles for Nobuhide and was assigned Narumi Castle at a strategic location on the provincial border to defend the southeast portion of Owari. After the death of Nobuhide in 1552, in the era of his son, Oda Nobunaga, Noritsugu abandoned the Oda in favor of the Imagawa and had his son, Yamaguchi Noriyoshi, defend Narumi Castle. He then established a fortress in Kasadera and brought in forces from Suruga such as Okabe Motonobu. Noritsugu himself remained in Sakuranakamura Castle. Noriyoshi subsequently engaged Nobunaga in the Battle of Akatsuka which resulted in a draw.
Noritsugu lured the lords of Ōdaka and Kutsukake castles away from the Oda to capture these sites. Later, however, after being summoned to Suruga, Noritsugu and his son, Noriyoshi, were forced, upon orders of Yoshimoto, to commit seppuku. Nobunaga may have orchestrated the deaths of Noritsugu and his son through deceptive tactics. Tobe Masanao, the lord of Tobe Castle in Owari, died under similar circumstances. Under one theory, he is the same individual as Noritsugu.