Me too..been there, done that, felt embarrassed and bruised...IT HURTS!!! It's because of the steel studs in the soles of the boots, put there to make the boots sound as you are marching, but they don't stick on concrete or tarmac, hence the fall on your bum. Incidentally the first time you have studs put in the soles of your boots the marching gets much much quicker, almost breaks into a run and you have to seriously think about keeping the marching speed the same as in rubber-soled boots...weird eh!