, "underpromotion" refers to the act of promoting a pawn
to a piece other than a queen
upon reaching the eighth rank--that is, promoting
to a knight
. One of the most frequent reasons for doing this is to avoid stalemating
the opponent, but there are many other plausible situations where underpromotion occurs. Underpromotion to a knight, for example, can be deadly if the newborn knight immediately fork
s the opponent's king
and queen from its promotion square. Underpromotion can even be a psychological tactic
, to emphasise to the opponent that a queen is not needed to defeat him, or (in cases where the promotion square is under attack) to make him unsure whether to capture the promoted piece.
For one of the most famous endgame positions in which underpromotion plays a vital role, see Saavedra position.