Projection is the thing some people do where they accuse someone else of something they themselves do, especially when there is no reason to suspect the accused. It could be considered a form of self-report.
An example might be if a racist individual (lets call them Bob) accuses someone of racism (Joe) because they crossed a street. Joe may have had plenty of valid reasons to cross the street; maybe they wanted to go into the shop across the street, maybe their car was parked on the other side, maybe they saw a friend and wanted to surprise them. Bob, however, being a racist fuck, sees Joe cross the street, sees a black man walking down the sidewalk that Joe just left, and immediately jumps to the conclusion that Joe was crossing the street to avoid the black dude. The reality is that Joe didn't even notice the black guy, but Bob, being a racist fuck, assumes that Joe is just doing the same thing that Bob would have done.
That is projection.
I'm not sure if that fully answers your question, though I will say I see people seemingly jump the gun a lot. Accusing someone of projecting is similar to accusing someone of arguing in bad faith; except instead of accusing them of arguing in bad faith, you're accusing them of making accusations "in bad faith", so to speak. However, like accusing someone of arguing in bad faith, some people will just use it to shut people down.