A method for determining a direction of a spin axis of a sports object when it is rotating, the sports object comprising a XYZ-magnetic field sensor , a control module and an accelerometer arranged inside of a body of the sports object, the method comprising: - detecting by the accelerometer that the sports object is ejected into a shot direction on a ballistic trajectory; - activating the XYZ-magnetic field sensor arranged inside of the body of the sports object when it is detected that the sports object is ejected on the ballistic trajectory; - determining a global direction of a magnetic field; - providing a rotation for the sports object about the spin axis, wherein the spin axis is defined along a line including points in a three-dimensional space which remain fixed during the rotation of the sports object; - measuring a plurality of magnetic field values as a function of time with the XYZ-magnetic field sensor when the sports object is rotating about the spin axis; - computing a magnetic field component of the magnetic field in a direction of a local body co-ordinate of the spin axis of the sports object when it is rotating from the measured plurality of magnetic field values; and - determining a direction of the spin axis using the computed magnetic field component of the magnetic field and the determined global direction of the magnetic field, wherein determining the direction of spin axis further comprises: - determining an angle of the spin axis with respect to the horizontal ground plane; and - determining an angle of the shot direction with respect to the horizontal component of the spin axis. - detecting by the accelerometer that the sports object is ejected into a shot direction on a ballistic trajectory; - activating the XYZ-magnetic field sensor arranged inside of the body of the sports object when it is detected that the sports object is ejected on the ballistic trajectory; - determining a global direction of a magnetic field; - providing a rotation for the sports object about the spin axis, wherein the spin axis is defined along a line including points in a three-dimensional space which remain fixed during the rotation of the sports object; - measuring a plurality of magnetic field values as a function of time with the XYZ-magnetic field sensor when the sports object is rotating about the spin axis; - computing a magnetic field component of the magnetic field in a direction of a local body co-ordinate of the spin axis of the sports object when it is rotating from the measured plurality of magnetic field values; and - determining a direction of the spin axis using the computed magnetic field component of the magnetic field and the determined global direction of the magnetic field, wherein determining the direction of spin axis further comprises: - determining an angle of the spin axis with respect to the horizontal ground plane; and - determining an angle of the shot direction with respect to the horizontal component of the spin axis. - determining an angle of the spin axis with respect to the horizontal ground plane; and - determining an angle of the shot direction with respect to the horizontal component of the spin axis. <EOS>