I found this one girl like this at dinner feeding time. It wasn't there 4 or less hours earlier, but now it's been there a couple hours. I don't think it's wet as it would've dried by now. It feels a bit dirty/crusty, nothing obvious...maybe somebody pooped on her? Or is this a sign she's being pecked at? I have not caught anyone pecking her.
What part of the chicken are we looking at? Can you take another picture where you pull back a bit so we can see the whole bird, to get some perspective on this? Have you tried cleaning this to see what it is and what's under the feathers? Is there an injury? How is she acting? Eating, drinking, pooping normally? Scratching, pecking, dust bathing? Can you feel her crop and describe how it feels? Full, empty, squishy, mushy, doughy, gritty, etc.?