I recall another clue somewhere (posted by someone else upthread iirc) using the same champion.
I guessed the solution quickly based on defn,. but discarded it until the chessplayer finally came to mind several minutes later.
In the "fair but difficult GK" category IMO. Unfair would be, say, using a "FIDE knockout" champion like Khalifman, Kasimdzhanov or Ponomariov. 🤣