Ancient human skeletal remains with stab injuries were excavated from the Zaimokuza site in Kamakura City, Japan. These excavated remains are considered to be those of warriors who died in action during the fall of the Kamakura shogunate in 1333. The specimen in the present study was most likely a male soldier (bushi) of early middle age. In this manuscript, the possible circumstances of injury and weapons that may have been used to inflict the injury are discussed. The size, shape and angle of the wound strongly suggested that it was caused by a spear (yari) rather than a sword, dagger or arrow. In Japan, spears (yari) were used beginning in the late Kamakura period. Computed tomographic scans revealed that the injury extended into the intracranial cavity, and it likely penetrated the dura mater and damaged the frontal lobe. Studies of injury marks in ancient skeletal remains can reveal details about ancient wars and what types of weapons were used. This field should be advanced with the collaboration of physical anthropology and philological history. Copyright © 2011 John Wiley & Sons, Ltd.