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. Said warning are yellow, orange or red colors or low, moderate and high frequency beeps or both.
