The other day I was entering the arena while mounted on my horse. I ducked to get under the metal bar that frames the doorway but did not duck enough and whacked my head on the bar. I was wearing my helmet so it did not really hurt. I know if you fall and hit your head you are supposed to replace your helmet... but what if you stupidly bang your head on a metal pole? Would the impact be enough to damage my helmet or should I not worry about it.