This topic was discussed at length on Barb's old website regarding recreational wrestling. Nursing was the occupation that claimed the most participants. When you think about it, it makes some sense. Nurses are used to making physical contact with other people, including strangers, and can't be shy about anything. Add to that any kind of competitive nature and you have the perfect mix of characteristics that would make for an avid wrestler.
I realize that your question was about catfighting and not wrestling, but I couldn't resist adding something that is somewhat pertinent.