Ah, yeah. Just this year I had quite a nasty fall involving my hakama. It was at a yudansha training session and I was uke for sensei. We were working at a vigorous pace when I was thrown by sensei. However, he had stood on my hakama in the process of doing his technique. So one leg was pinned as I rolled at high speed. Needless to say, I didn't finish my roll and I felt pain shoot through the top of my butt and my lower back as I was twisted.
As it turns out, a muscle deep in my buttocks took the brunt of the accident and not my lower spine! So my hakama has been responsible for a torn butt muscle