I have been a victim of it and seen it on others many times. It's a flesh eating bacteria that is a relative of staph, usually come from lack of proper hygiene. Most times I have seen it was on elbows and knees and rarely hips. Mostly places that would get a lots of friction from clothes. Like I said in the military we would go to the field and people (the nasty mother fuckers) wouldn't wash the cammies they spent all hours of the day in sweating there ass off while not having the ability to shower. It was almost a guarantee someone would get it. If you wear a Gi, I recommend wearing a rash guard and tights underneath. Most of all proper hygiene is the best way to avoid this nasty shit. Shower after every practice as soon as possible and never sit around at home in clothes you just worked out in. If you have it and it's really bad, go see a doctor and they will lance out the infection and perscibe you antibiotics. It's really contagious too so don't go rolling with people with it either, if you wait to take care of it can become MRSA and it could be really serious at that point. See a doctor they will help get rid of it.