A football helmet comprises a rotatable outer shell, an inner shell and a fastener assembly. The inner shell comprises an upper portion and a lower portion. The rotatable outer shell is of a hollow hemisphere shape. The rotatable outer shell has a cavity to receive the upper portion of the inner shell. An air gap is between the upper portion of the inner shell and the rotatable outer shell. A pre-determined torque is applied to a nut of the fastener assembly so that the nut is loosely tightened to a bolt of the fastener assembly. The rotatable outer shell is in a pogo stick motion when a force is applied to the rotatable outer shell so that the ring rotates along the rim track and an outer shell hole deflects toward an inner shell hole.