In 1333, when an army led by Yoshisada NITTA, who was a gokenin (an immediate vassal of the shogunate in the Kamakura and Muromachi through Edo periods) of Kozuke Province, invaded Kamakura in response to the rise of the Emperor Godaigo, Sadayuki led the Battle of Tsurumi as a general of the army of the bakufu (Japanese feudal government headed by a shogun) and after retreating to Kamakura, he defended at Kobukuro-zaka Slope.
元弘3年（1333年）、後醍醐天皇の挙兵に呼応して、上野国の御家人新田義貞の率いる新田軍が鎌倉に侵攻すると、幕府軍の大将として鶴見の戦い、鎌倉へ敗退した後には巨福呂坂を防備する。