Abstract: Method for warning a coach in real-time that a team player suffered head injuries why playing on a sports field with other players present, comprising the steps of: having the player wear a headband with one battery powered multi-axial motion sensor mounted on the rear; measuring with the sensor 3-D (X-Y-Z) accelerations out of which 2-D (X-Y) is in essentially horizontal plane when the player is standing facing forward; establishing head bank, roll and yaw angular acceleration thresholds for mild, moderate and severe head injuries; having an applet calculate the angular accelerations form the linear accelerations or measure angular accelerations directly; comparing measured angular accelerations to threshold angular accelerations; warn the coach about the occurrence of threshold exceedances indicating mild, moderate or severe head injuries; log the time of the threshold exceedances along with the measured values of the angular accelerations.