A
chess term, from the
German for "in-between move".
Zwischenzug refers to a
move which is unexpectedly inserted in the middle of an apparently
forced sequence of moves. Perhaps the most common circumstance where a zwischenzug arises is during a trade of pieces; a player may capture a piece, expecting an immediate recapture, when in fact his opponent can seize the initiative by playing an attacking move before recapturing. Here is an example position where Black falls prey to a zwischenzug:
+---+---+---+---+---+---+---+---+
| | |BK | | | | | |
+---+---+---+---+---+---+---+---+
|BP |BP |BP | | | | | |
+---+---+---+---+---+---+---+---+
| | | |BQ |BB | |BR | |
+---+---+---+---+---+---+---+---+
| | | | |WQ | | |BN |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | |WN | |WR | | |
+---+---+---+---+---+---+---+---+
| | | | | | |WP |WP |
+---+---+---+---+---+---+---+---+
| | | | | |WK | | |
+---+---+---+---+---+---+---+---+
Here Black, since he is ahead on material, decides to trade off queens and rooks to enter a favourable
endgame. He plays
1. ...Qxe5?? expecting the knight to recapture, when he could play
Rf6 forcing the exchange of rooks. White, however, finds
2. Rf8+!, forcing the king to d7, after which
3. Nxe5+ wins Black's rook. (It is quite common for the zwischenzug to be a move giving
check; the
German term for this is
zwischenschach, meaning "in-between check".)
The moral: assume nothing at the chessboard; quickly calculate the variations even in an "obvious" sequence of moves, lest your opponent surprises you with a tactic like that above.