Judo has high mortality rate than other sports, and the most common cause of death has been reported to be acute subdural hematoma caused by osoto-gari (large outer reap). The purpose of this study was to analyze the head movement of the uke (the person being thrown) of osoto-gari for examination of the mechanism of acute subdural hematoma caused in judo activity. In our experiment, the uke wear a headgear equipped with angular rate sensor to measure the angular velocity in the sagittal direction of the head of the uke at the time when the tori (the person who throws) threw by osoto-gari and calculated the angular acceleration. We used a high-speed camera to record behaviors of the tori and the uke. No marked change in the angular acceleration was observed when the uke was in the air from the time when he was thrown to the time when he did ukemi (breaking the fall). The peak angular acceleration was observed just after the palms made contact with the floor. Head movement of ushiro-ukemi (rear breakfall) was analyzed similarly. Also, in ushiro-ukemi, the peak angular acceleration was observed just after the palm made contact with the floor. However, each value was smaller than the threshold value of rupture of a bridging vein. The results showed that having the hand make contact with the floor and reduced the angular acceleration of the head and prevented excess rotation backward.