- I'll assume you mean OTB, because online no one would notice or care.
- Masters play non-masters all the time.
- Just normal mistakes.
- It's not uncommon to lose 100 or 200 points.
- "I had a spark of brilliancy but then lost it all" makes no sense.
So, imagine you became a master. Most players do not. How would you ever properly go back and lose rating to play in those sub par under 2100 rated tournaments. What type of mistakes would you have to make willingly to lose? Would it be that believable? Say a 2300 dropping to 2100 in a few months? Or would the guy be labeled off as a cheater.
Maybe his excuse would be like: "he had a spark of brilliancy but then lost it all?"