When I take photos at wrestling tournaments, I don't use a flash; it is distracting to the athletes. This means I'm using the gym's "natural lighting," which is minimal in many cases.
For the photographers among you, I set my camera, an Olympus C-2100 UZ, to an ISO level of 400, EV to +0.3, and shutter priority at 1/40 of a second to get as much light in as possible.
In addition to the low light levels, the light in this gym has a very distinct yellow cast to it. This means that pictures come out looking very strange indeed:
I can adjust color levels to get the flesh tones and mat colors back to something near normal, but it's still too dark.
Lightening up the picture works, but it's still not "right." Furthermore, each time you do a transformation to a picture, you spread out (or at worst, lose) information. This adds "noise" to a picture which was grainy to begin with.
Rather than make a huge effort to salvage what is nearly a lost cause, it's easier to simply discard the color information altogether. The pictures then need only be lightened up, which takes a single extra transformation. And that's why some of these pictures are in black and white.
You'll notice that some of the pictures are in color; those were taken during finals, when the mat was lit with spotlights that had a normal spread of the spectrum instead of being concentrated in the yellow.
Page 114