user8063: Is it unsportsmanlike to underpromote a pawn to improve my chances? Sometimes I reach a won endgame where underpromoting my pawn will result in a slower but easier final checkmate.
Old example, easiest to understand: I was far better practiced at K-R vs K than K-Q vs K so I promoted a lone pawn to a rook. Improvising K-Q vs K would have had too high of stalemate chance for my taste.
Recent example: I deliberately underpromoted a pawn to a rook rather than a queen while having a queen. This makes mate in 9 moves worst case rather than 8 and again reduces the accidental stalemate odds dramatically.
I barely care about my opponent not resigning when he should. Primary reason: I once played out a losing game, sacrificing my last piece to push the ending int B-N endgame. My opponent said I should resign as he had a book endgame. I said, "Yes, but I don't think you can do it." Fifty move rule got him: B-N is tight and he was out of practice.

user14760: Here's a game with pawn promotion to a Knight for checkmate.  Nothing unsportsmanlike when one plays to win as far as I am concerned.
Zvonimir Mestrovic vs Svetozar Gligoric
https://lichess.org/RiMAvMwD

user11245: You may choose any legal move you like; your opponent's sole recourse is to prove that it wasn't good enough.
This also applies to fighting on in lost games. There is always the possibility that the opponent will blunder away their advantage, or even the game itself.
I applied this principle when faced with an opponent with a bare king who refused to resign. I promoted my two pawns to knights for a total of three, and delivered a novel checkmate with K+3N. (The theory is known, apparently but I couldn't find any other examples so I developed my own).
It was a lot more challenging than just ginning up a simple Q+R mate, and even drew a small audience.

user8860: Underpromotion might be "unsportsmanlike" if you do it toy with your opponent
(e.g. promoting several pawns to Bishops for the heck of it),
but if you do it to make the win easier then there's absolutely nothing
wrong with it, even if it's because you're more comfortable winning with
KR/K than KQ/K (which must be very unusual, but is not
a failure of sportsmanship).
Tim Krabbé has a nice collection of examples of promotion to R or B
in actual play: https://timkr.home.xs4all.nl/chess2/minor.htm .
In a few cases the underpromotion is the only winning move,
or at least the only winning promotion (because Q would stalemate
and N is not strong enough).  But there are also cases where
a Queen would win too but with more difficulty because you must
deal with a stalemate defense -- close to what you describe
albeit at a higher level of play.  See the four examples introduced by

in all of the following examples promotion to Queen would also have worked.
But sometimes it would have been tricky, and in most cases the Rook promotion
was the most sensible and practical thing to do:
why think if you don't have to.


user7002: It's ok, top players do it too. But be prepared to face the consequence when the underpromotion doesn't work out.
http://www.chessgames.com/perl/chessgame?gid=1879525
(Move 77... f1=N by Nakamura)

user12629: If, as you say, you are "improving your chances", then it's not unsportsmanlike.  Even if your opponent misunderstands, he doesn't really have much to complain about - if he doesn't want to play on he is free to resign.

I barely care about my opponent not resigning when he should.

Good, because demanding that your opponent resign IS unsportsmanlike.

8063: <p>Is it unsportsmanlike to underpromote a pawn to improve my chances? Sometimes I reach a won endgame where underpromoting my pawn will result in a slower but easier final checkmate.</p>

<p>Old example, easiest to understand: I was far better practiced at K-R vs K than K-Q vs K so I promoted a lone pawn to a rook. Improvising K-Q vs K would have had too high of stalemate chance for my taste.</p>

<p>Recent example: I deliberately underpromoted a pawn to a rook rather than a queen while having a queen. This makes mate in 9 moves worst case rather than 8 and again reduces the accidental stalemate odds dramatically.</p>

<p>I barely care about my opponent not resigning when he should. Primary reason: I once played out a losing game, sacrificing my last piece to push the ending int B-N endgame. My opponent said I should resign as he had a book endgame. I said, "Yes, but I don't think you can do it." Fifty move rule got him: B-N is tight and he was out of practice.</p>
 14760: <p>Here's a game with pawn promotion to a Knight for checkmate.  Nothing unsportsmanlike when one plays to win as far as I am concerned.</p>

<p>Zvonimir Mestrovic vs Svetozar Gligoric</p>

<p><a href="https://lichess.org/RiMAvMwD" rel="nofollow noreferrer">https://lichess.org/RiMAvMwD</a></p>
 11245: <p>You may choose any legal move you like; your opponent's sole recourse is to prove that it wasn't good enough.</p>
<p>This also applies to fighting on in lost games. There is always the possibility that the opponent will blunder away their advantage, or even the game itself.</p>
<p>I applied this principle when faced with an opponent with a bare king who refused to resign. I promoted my two pawns to knights for a total of three, and delivered a novel checkmate with K+3N. (The theory is known, apparently but I couldn't find any other examples so I developed my own).</p>
<p>It was a lot more challenging than just ginning up a simple Q+R mate, and even drew a small audience.</p>
 8860: <p>Underpromotion might be &quot;unsportsmanlike&quot; if you do it toy with your opponent
(e.g. promoting several pawns to Bishops for the heck of it),
but if you do it to make the win easier then there's absolutely nothing
wrong with it, even if it's because you're more comfortable winning with
KR/K than KQ/K (which must be very unusual, but is not
a failure of sportsmanship).</p>
<p>Tim Krabbé has a nice collection of examples of promotion to R or B
in actual play: <a href="https://timkr.home.xs4all.nl/chess2/minor.htm" rel="noreferrer">https://timkr.home.xs4all.nl/chess2/minor.htm</a> .
In a few cases the underpromotion is the only winning move,
or at least the only winning promotion (because Q would stalemate
and N is not strong enough).  But there are also cases where
a Queen would win too but with more difficulty because you must
deal with a stalemate defense -- close to what you describe
albeit at a higher level of play.  See the four examples introduced by</p>
<blockquote>
<p>in all of the following examples promotion to Queen would also have worked.
But sometimes it would have been tricky, and in most cases the Rook promotion
was the most sensible and practical thing to do:
why think if you don't have to.</p>
</blockquote>
 7002: <p>It's ok, top players do it too. But be prepared to face the consequence when the underpromotion doesn't work out.</p>

<p><a href="http://www.chessgames.com/perl/chessgame?gid=1879525" rel="noreferrer">http://www.chessgames.com/perl/chessgame?gid=1879525</a></p>

<p>(Move 77... f1=N by Nakamura)</p>
 12629: <p>If, as you say, you are "improving your chances", then it's not unsportsmanlike.  Even if your opponent misunderstands, he doesn't really have much to complain about - if he doesn't want to play on he is free to resign.</p>

<blockquote>
  <p>I barely care about my opponent not resigning when he should.</p>
</blockquote>

<p>Good, because demanding that your opponent resign IS unsportsmanlike.</p>
