@StingerPuzzles said in #5:
> The knight was doing nothing useful on a5. You can't be deflected from nothing. For a deflection tactic to occur a piece has to be doing something useful on its original square.
Why, it was attacking an entire queen! And after it was successfully deflected, it no longer played such a useful role as attacking a valuable piece! :-)
To answer the OP’s question, I think the situation is best described as a trap: an unforced move that looks appealing on the surface but that worsens the position instead.
Much like the Légal Trap, the white queen is not a part of the tactic at all: the attacking player threatens mate, and if the other player reacts by capturing an irrelevant piece, they have fallen into the trap. So this is not a sacrifice, because when you sacrifice a piece, you destroy the opponent’s pawn structure, or capture a minor but very well placed piece, or force the king to end up in just the right square etc.—the act of the sacrifice immediately provides you with some compensation, which you hope you can exploit all the way to a win.