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Comment by dkarl | Hacker News Reader

I played chess for only a few years, at a low level, and I encountered situations where underpromotion to a bishop or rook was necessary to win. It's possible it is more common at the just-above-beginner level than at the elite level, because a player in a losing position will play on longer and try to set up stalemate traps that would be pointless in higher-level games.

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The unspoken assumption here would be promoting to rook or bishop "instead of a queen" and as the post points out other than avoiding the stalemate situation there doesn't appear to be a logical reason for doing this.

It probably wouldn’t ever happen in a real game, but I think it’s possible to be in a situation where you’re still losing after promoting to a queen, but underpromoting to a bishop forces a stalemate by leaving you with no legal moves no matter what your opponent plays in response.

Indeed it wouldn't happen in a game but ... I easily created a position where promotion to a bishop is stalemate after any black move (confirmed by Stockfish):

White pawns on a7 and b7, king on h8. Black king on f2, bishop on g3, rook on h3, knights on a6 and b8, pawns on c6, d7, f3, and h2.

This position is a draw after a8=Q or axb8=Q but that is easily remedied by adding black pieces, e.g., a queen on h4.

There are puzzles where only a bishop promotion wins. The others are either forced stalemate or forced draw by repitition. Finding a real game where that happens is unlikely

The definition of a "real game" gets extremely relaxed in a competitive situation between low-rated players. Between two grandmasters, they're going to stop the moment the outcome becomes clear. But when you have two just-above-beginners, there are other factors. They're going to keep playing in lost positions where there's a big material imbalance. They're going to miss a lot of mates in 3+ moves, and even simpler mates under time pressure. They end up in weird and "unrealistic" positions that aren't even interesting as puzzles, but have competitive significance to them because if the player with a big positional or material advantage loses on time or makes a blunder under time pressure, it will affect their rating and their standing in a tournament.

Theoretically you could devise a scenario where promoting to a bishop would forcefully draw an otherwise losing position.

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