The Kage nagu-gumi (影殴組, "Shadow Strike Brigade" or "Shadow Assault Group"), sometimes called the Kyō kei-gumi (京警組, "Capital Police Group") was a group of samurai founded by Usami Chūhei that were ordered to "keep the peace" around Kyoto following the usurpation of the Ashikaga Shogunate by the Horiuchi clan. Although superficially enforcers of the Horiuchi's will, in reality the group was loyal only to Chūhei and his liege lord, Sakai Hirochika. The group patrolled the streets of the capital during the day, serving as police officials and bearing either insignias or sashimonos of the Sakai and Horiuchi clans. During the nights, however, they donned simple clothing with no identifying mons and attacked anti-Horiuchi establishments or persons, hence their more common colloquial name.
Founded some time in 1562, the group was commanded to maintain order within Kyoto after the Horiuchi clan attained power. The clan leader, Ujitora, convinced Emperor Ōgimachi to name the Horiuchi as enforcers of Imperial will in favour of the Ashikaga, who he argued had lost control of the country. Supported by the Sakai and Yusa clans amongst others, the Horiuchi nonetheless faced opposition from rival clans most notably the Kitabatake. Kitabatake Harumoto, years earlier had sent ten of his most skilled sword-students to the capital as a gift to Ashikaga Yoshiteru and they had formed an elite bodyguard around the shōgun. After the usurpation of the shogunate, Yoshiteru continued to fight in order to maintain his position of authority with Harumoto's students serving as his agents within Kyoto. They named themselves the Kyō kei-gumi in opposition to Chūhei's unit and fought openly with Horiuchi-supporting samurai and establishments within the capital.
Most famously, the two groups clashed over the Niomon-dori and Nijo-dori bridges in what became known as the Saishōji-chō Incident. After fierce fighting, the Kagu nagu-gumi managed to outmanoeuvre and overwhelm their rivals, slaughtering most of them, including two of their most prominent leaders.