A heel-piece of a ski binding, wherein: it comprises a base which is fixable to a ski; it comprises an annular wall which extends from the base and which comprises an internal side; it comprises a support which is rotatably borne by the annular wall; it comprises at least a first hooking and unhooking terminal which is borne by the support and which is suitable for hooking to the rear portion of a ski boot and for unhooking from the rear portion of the ski boot; it comprises a clutch member; it comprises elastic means which are borne by the support; wherein: the annular wall comprises a first seat arranged on the relative internal side; it comprises a rocker arm which is rotatingly borne by the support; the clutch member is borne by the rocker arm, faces the internal side of the annular wall and is conformed to engage in the first seat and to slide along the internal side of the annular wall; the elastic means are arranged so as to press against the rocker arm in such a way that the clutch member in turn presses against the internal side of the annular wall; the heel-piece is designed in such a way that starting from a ski descent configuration, in which the at least a first hooking and unhooking terminal is hooked to the rear portion of the ski boot and the clutch member engages in the first seat, so that it is possible to ski downhill, a first unhooking torque acting on the at least a first hooking and unhooking terminal and greater than a predetermined first threshold value can determine a rotation of the support against the action of the elastic means, with a consequent: disengagement of the clutch member from the first seat and a sliding of the clutch member along the internal side of the annular wall; and the unhooking of the at least a first hooking and unhooking terminal from the rear portion of the ski boot. it comprises a base which is fixable to a ski; it comprises an annular wall which extends from the base and which comprises an internal side; it comprises a support which is rotatably borne by the annular wall; it comprises at least a first hooking and unhooking terminal which is borne by the support and which is suitable for hooking to the rear portion of a ski boot and for unhooking from the rear portion of the ski boot; it comprises a clutch member; it comprises elastic means which are borne by the support; wherein: the annular wall comprises a first seat arranged on the relative internal side; it comprises a rocker arm which is rotatingly borne by the support; the clutch member is borne by the rocker arm, faces the internal side of the annular wall and is conformed to engage in the first seat and to slide along the internal side of the annular wall; the elastic means are arranged so as to press against the rocker arm in such a way that the clutch member in turn presses against the internal side of the annular wall; the heel-piece is designed in such a way that starting from a ski descent configuration, in which the at least a first hooking and unhooking terminal is hooked to the rear portion of the ski boot and the clutch member engages in the first seat, so that it is possible to ski downhill, a first unhooking torque acting on the at least a first hooking and unhooking terminal and greater than a predetermined first threshold value can determine a rotation of the support against the action of the elastic means, with a consequent: disengagement of the clutch member from the first seat and a sliding of the clutch member along the internal side of the annular wall; and the unhooking of the at least a first hooking and unhooking terminal from the rear portion of the ski boot. the annular wall comprises a first seat arranged on the relative internal side; it comprises a rocker arm which is rotatingly borne by the support; the clutch member is borne by the rocker arm, faces the internal side of the annular wall and is conformed to engage in the first seat and to slide along the internal side of the annular wall; the elastic means are arranged so as to press against the rocker arm in such a way that the clutch member in turn presses against the internal side of the annular wall; the heel-piece is designed in such a way that starting from a ski descent configuration, in which the at least a first hooking and unhooking terminal is hooked to the rear portion of the ski boot and the clutch member engages in the first seat, so that it is possible to ski downhill, a first unhooking torque acting on the at least a first hooking and unhooking terminal and greater than a predetermined first threshold value can determine a rotation of the support against the action of the elastic means, with a consequent: disengagement of the clutch member from the first seat and a sliding of the clutch member along the internal side of the annular wall; and the unhooking of the at least a first hooking and unhooking terminal from the rear portion of the ski boot.