What Is Underpromotion in Chess?
This is when you are promoting a pawn to something other than a queen when they have made it to the last rank.
You can choose a:
- Knight (=N)
- Rook (=R)
- Bishop (=B)
Of course, you can still choose a queen (=Q). In most positions, that will be the obvious choice.
The knight may be the most interesting option. Differing from other pieces, it doesn't move straight but in an L shape, in a way the queen cannot. This is a clear reason why the knight promotion can be very useful in certain tactical positions.
When Underpromotion Is the Better Choice
But why does anyone deliberately turn a pawn into a weaker piece? I hear you ask.
Simply put, it's to avoid a stalemate.
Imagine you are completely winning. The opposing king doesn't have any legal moves and your pawn is a single move away from the last rank. Promoting to a queen might leave the king with no legal move — but without being in check. Suddenly, your winning game is a draw.
A knight promotion can sometimes give the king a square to escape to.
There are tactical reasons, too. A knight can give a check immediately after promotion or create a fork against two pieces. Extra possibilities can be more important than having the strongest piece on the board in positions where exact movement is key.
Hence why it is worth having knowledge of underpromotion, even if it rarely occurs in a regular game.
Famous Underpromotion Examples
The classic example is the knight promotion to avoid stalemate.
It often comes up in composed endgame positions where one side has carefully trapped the opposing king. A queen would finish the job too efficiently and leave no legal moves. Promoting to a knight changes the position just enough to keep the game going.
There are also famous examples where a knight promotion delivers a check or creates a decisive fork. These moves tend to stick in players' memories because the winning idea is so easy to miss.
If you have a pawn ready to promote, it is worth taking an extra second before clicking the queen. Ask yourself what each promotion actually does.
Conclusion
Underpromotion is rare, but that is exactly what makes it so satisfying when it appears.
The queen will usually be the right answer, but it isn't always. Other pieces can deliver a check as well, from a knight to a rook, something other than a queen might be the correct answer depending on the position.
It may be a small part of chess, but a very useful one to know if you are looking for a full repertoire of chess knowledge. Maybe then the next time your pawn is about to be promoted you’ll find yourself looking at all four choices instead of automatically choosing the queen.