an energy absorbing ball comprising a resilient structural outer casing and an energy absorbent core , characterized in that the core is formed of a non - resilient deformable material adapted on rolling to move relative to the casing . the core may comprise , in part , a low viscosity liquid and a surface active agent . the inner surface of the casing is smooth and the deformable material consists by volume of from 40 - 70 % of the core volume , thereby to provide an average deviation on striking of less than 0 . 21 meters per meter run .