Sadamasa's decision to remove himself and his forces from the Takeda supporters became one of the antecedents of the Battle of Nagashino in 1575. Katsuyori was enraged at Sadamasa's decision to leave the Takeda forces. Nagashino Castle was attacked by Katsuyori with a force of 15,000 troops; but Sadamasa held firm, repelling the Takeda siege until forces of a Tokugawa-Oda alliance eventually arrived to support the beleaguered Okudaira. Oda Nobunaga was so impressed by the Okudaira's performance in the battle that he offered Sadamasa the honor of adopting part of his name—Nobu. After the battle was won, the hardy warrior was changed from Sadamasa to Nobumasa.