https://en.wikipedia.org/wiki/Chess_tactic
In chess, a tactic refers to a sequence of moves that limits the opponent's options and may result in tangible gain. Tactics are usually contrasted with strategy, in which advantages take longer to be realized, and the opponent is less constrained in responding.
The fundamental building blocks of tactics are move sequences in which the opponent is unable to respond to all threats, so the first player realizes an advantage. This includes forks, skewers, batteries, discovered attacks, undermining, overloading, deflection, pins, and interference. The Encyclopedia of Chess Middlegames gives the following tactics categories: Double Attack, Pawns Breakthrough, Blockade, Decoying, Discovered Attack, Passed Pawn, X-ray Attack, Interception, Deflection, Pin, Demolition of Pawns, Overloading, Annihilation of Defense, Pursuit (perpetual attack), Intermediate Move, and Space Clearance.
Often tactics of more than one type are conjoined in a combination.
In chess, a tactic refers to a sequence of moves that limits the opponent's options and may result in tangible gain. Tactics are usually contrasted with strategy, in which advantages take longer to be realized, and the opponent is less constrained in responding.
The fundamental building blocks of tactics are move sequences in which the opponent is unable to respond to all threats, so the first player realizes an advantage. This includes forks, skewers, batteries, discovered attacks, undermining, overloading, deflection, pins, and interference. The Encyclopedia of Chess Middlegames gives the following tactics categories: Double Attack, Pawns Breakthrough, Blockade, Decoying, Discovered Attack, Passed Pawn, X-ray Attack, Interception, Deflection, Pin, Demolition of Pawns, Overloading, Annihilation of Defense, Pursuit (perpetual attack), Intermediate Move, and Space Clearance.
Often tactics of more than one type are conjoined in a combination.
Attacking and defending pieces
A piece is said to attack (or threaten) an opponent's piece if, in the next move, it could capture that piece. A piece is said to defend
(or protect) a piece of the defender's color if, in case the defended
piece were taken by the opponent, the defender could immediately
recapture. Attacking a piece usually, but not always (see Sacrifice),
forces the opponent to respond if the attacked piece is undefended, or
if the attacking piece is of lower value than the one attacked.
When the piece attacked is a king, then a player has exactly three options:
- capture the attacking piece;
- move the king to a free square;
- interpose another piece in between the two (if the attacker is not a knight and is not directly adjacent to the king attacked).
When the piece attacked is not a king, a player has more options:
- capture the attacking piece;
- move the attacked piece to a free or covered square;
- move the attacked piece to a different attacked square, so you can choose where the capturing happens;
- interpose another piece in between the two (if the attacker is not a knight and is not directly adjacent to the piece attacked - attacking kings and pawns are adjacent always);
- cover the attacked piece, permitting an exchange of equal, greater, or lower value;
- pin the attacking piece so the capture becomes illegal, unprofitable, or less damaging;
- capture a different piece of the opponent;
- allow the piece attacked to be captured, a sacrifice, for some other tactical advantage; or for Tempo
- employ a zwischenzug (create a counter-threat of equal, greater, or lesser consequence).
Gaining material
When
a player is able to capture the opponent's piece(s) without losing any
of their own (or losing a piece of lesser value), the player is said to
have "won material";
i.e., the opponent will have fewer (or less valuable) pieces remaining
on the board. The goal of each basic tactic is to win material. At the
professional level, often the mere threat of material loss (i.e., an
anticipated tactic) induces the opponent to pursue an alternative line.
In amateur games, however, tactics often come to full fruition –
unforeseen by the opponent and resulting in material gain and a
corresponding, perhaps decisive, advantage. Material gain can be
achieved by several different types of tactics.
Discovered attack
A discovered attack is a move which allows an attack by
another piece. A piece is moved away so as to allow the attack of a
friendly bishop, rook or queen on an enemy piece. If the attacked piece
is the king, the situation is referred to as a discovered check. Discovered attacks are powerful since the moved piece may be able to pose a second threat.
A special case of a discovered check is a double check,
where both the piece being unmasked and the piece being moved attack the
enemy king. A double check always forces the opponent to move the king,
since it is impossible to defend attacks from two directions in any
other way.
Fork
| a | b | c | d | e | f | g | h | ||
| 8 |              | 8 | |||||||
| 7 | 7 | ||||||||
| 6 | 6 | ||||||||
| 5 | 5 | ||||||||
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| 2 | 2 | ||||||||
| 1 | 1 | ||||||||
| a | b | c | d | e | f | g | h | ||
Kasparov has played 12.Nc7+, forking Black's king and a8-rook.
A fork is a move that uses one piece to attack two many are mistaken with knife or more of the opponent's pieces simultaneously, with the aim to achieve material advantage, since the opponent can counter only one of the threats. Knights are often used for forks, with their unique moving and jumping ability. A common situation is a knight played to c2 or c7, threatening both the enemy rook and king. Such forks checking a king are particularly effective, because the opponent is forced by the rules of chess to immediately remove the check to his king. The opponent cannot choose to defend the other piece, or use a zwischenzug to complicate the situation. Pawns can also be effective in forking. By moving a pawn forward, it can attack two pieces—one diagonally to the left, and another diagonally to the right.
The queen
is also an excellent forking piece, since she can move in eight
different directions. However, a queen fork is only useful if both
pieces are undefended, or if one is undefended and the other is enemy
king. The queen is the most valuable attacking piece, so it is usually
not profitable for her to capture a defended piece.
Fork attacks can be either relative (meaning the attacked pieces comprise pawn[s], knight[s], bishop[s], rook[s], or queen[s]), or absolute
(one of the attacked pieces is the enemy king, in check). The targets
of a fork do not have to be pieces, although this is known as a double attack.
One or more of the targets can be a mate threat (for example, forking a
loose knight and setting up a battery of queen and bishop that creates a
mate threat as well) or implied threat (for example, a knight move that
forks a loose bishop and also threatens to fork enemy queen and rook).
Pin
| a | b | c | d | e | f | g | h | ||
| 8 | | 8 | |||||||
| 7 | 7 | ||||||||
| 6 | 6 | ||||||||
| 5 | 5 | ||||||||
| 4 | 4 | ||||||||
| 3 | 3 | ||||||||
| 2 | 2 | ||||||||
| 1 | 1 | ||||||||
| a | b | c | d | e | f | g | h | ||
Position after 14.Rd1. Morphy has a relative pin on Black's knight and an absolute pin on the d7-rook.
A pin is a move that inhibits an opponent piece from moving,
because doing so would expose a more valuable (or vulnerable) piece
behind it. Only bishops, rooks, and queens can perform a pin, since they
can move more than one square in a straight line. If the pinned piece
cannot move because doing so would produce check, the pin is called absolute. If moving the pinned piece would expose a non-king piece, the pin is called relative.
Skewer
A skewer is a move which attacks two pieces in a line, similar
to a pin, except that the enemy piece of greater value is in front of
the piece of lesser value. After the more valuable piece moves away, the
lesser piece can be captured. Like pins, only queens, rooks, and
bishops can perform the skewer, and skewer attacks can be either absolute (the more valuable piece in front is the king, in check) or relative (the piece in front is a non-king piece).
Example of an absolute skewer attack
Pawns
Pawns are the least valuable
chess piece, so are often used to capture defended pieces. A single
pawn typically forces a more powerful piece, such as a rook or a knight,
to retreat. The ability to fork two enemy pieces by advancing a pawn
is often a threat. Or a simple pawn move can reveal a discovered attack. When pawns are arranged on a diagonal, with each pawn guarded by the pawn behind it, they form a wall or pawn chain protecting any friendly pieces behind them. A weak pawn structure, with unprotected or isolated pawns
ahead of more valuable pieces, can be a decisive weakness. A pawn that
has advanced all the way to the opposite side of the board is promoted to any other piece except a king.
Sacrifices
| a | b | c | d | e | f | g | h | ||
| 8 | | 8 | |||||||
| 7 | 7 | ||||||||
| 6 | 6 | ||||||||
| 5 | 5 | ||||||||
| 4 | 4 | ||||||||
| 3 | 3 | ||||||||
| 2 | 2 | ||||||||
| 1 | 1 | ||||||||
| a | b | c | d | e | f | g | h | ||
Colle played 12.Bxh7+, an example of the so-called Greek gift sacrifice.
A sacrifice of some material is often necessary to throw the
opponent's position out of balance, potentially gaining positional
advantage. The sacrificed material is sometimes later offset with a
consequent material gain. Pawn sacrifices in the opening are known as gambits; they are usually not intended for material gain, but rather to achieve a more active position.
Direct attacks against the enemy king
are often started by sacrifices. A common example is sacrificing a
bishop on h2 or h7, checking the king, who usually must take the bishop.
This allows the queen and knight to develop a fulminant attack.
Zugzwang
Zugzwang (German for the "compulsion to move") occurs when a
player is forced to make an undesirable move. The player is put at a
disadvantage because he would prefer to pass and make no move, but a
move has to be made, all of which weaken his position. Situations
involving zugzwang occur uncommonly, but when they do occur, it is
almost always in the endgame, where there are fewer choices of available moves.
Zwischenzug
Zwischenzug (German for "intermediate move") is a common
tactic in which a player under threat, instead of directly countering,
introduces an even more devastating threat. The tactic often involves a
new attack against the opponent's queen or king. The opponent then may
be forced to address the new threat, abandoning the earlier attack.
The concept of a zwischenzug is often listed as a tactic, but
might properly be called a counter-tactic instead. The effect of a
zwischenzug is to change the status quo before a tactic can come to
fruition. The near ubiquity of the zwischenzug makes long combinations
all the more rare and impressive.
