# Chess/Tactics

## Guarding

When one of your pieces is placed so that it attacks a square occupied
by another of your pieces, the former is said to be guarding the latter.
When your opponent captures the guarded piece, you can recapture with
the guarding piece. Note that if a guarding piece is pinned to your king
(see below for a description of pins), it can only guard other pieces
against capturing by the enemy king, but not from other enemy pieces,
since it is unable to move or capture.

## Batteries

Batteries are formed when two or more pieces work together. The most
common kind of battery is the doubling of rooks on a file. Other
batteries can be formed by rook-queen, bishop-queen, two knights or a
bishop-pawn.

A triple battery can be constructed with the queen and both rooks. This
is known as Alekhine\'s gun
(diagram at right) and can be extremely dangerous. It is often
advantageous to place the queen behind one or both rooks as it is a more
valuable piece.

## The Exchange

In almost any game, a player will have the opportunity to capture one of
his opponent\'s pieces in exchange for sacrificing or losing one of his
own pieces. This should however NOT be done for its own sake! Initiate
an exchange only when it benefits you. Benefits can include, but are not
limited to:

-   Material advantage - Exchanging one of your pieces for a more
    valuable opponent\'s piece (e.g. exchanging a bishop for your
    opponent\'s Queen).
-   Doubling pawns - Take when taking back means the doubling (or
    tripling) of your opponent\'s pawns on the same file.
-   Opening up the king\'s defenses - Take when taking back means moving
    a pawn that exposes the king.
-   Removing a defender - Take when the piece being taken is providing
    an essential service for the opponent.
-   Blunting an attack - When you are being attacked, often a well timed
    exchange will leave your opponent with too few pieces to keep up the
    attack.
-   Gaining space - In a cramped position, having more pieces can
    actually be a disadvantage because the pieces get in the way of each
    other. If your opponent has a space advantage, exchanging pieces can
    lessen the advantage and make the resultant position less confining.
-   Improving a material advantage - if you are ahead material,
    exchanging pieces will usually benefit you (note - pieces, NOT
    pawns). Similarly, if you have an extra pawn, trade pieces that may
    otherwise be used as a sacrifice to prevent pawn promotion.
-   Forcing checkmate - If you are able to force a checkmate by
    exchanging pieces, you should always take the exchange, even if the
    exchanges seem poor (e.g. sacrificing a Queen for a bishop). Note
    that a forced checkmate is one where there is no way for your
    opponent to prevent the checkmate.
-   Threatening checkmate - Sometimes, you can propose an exchange where
    you can force a checkmate if your opponent accepts the exchange.
    That is if your opponent captures your piece after you capture one
    of their pieces, you are then able to force a checkmate.
-   Preventing checkmate - If you are in a situation where the only way
    out of a checkmate is to exchange pieces, you must make the
    exchange.

## Forks and Double Attacks

Sometimes a piece can be in position to attack two enemy pieces at once.
This is called a fork or a double attack. All pieces can fork, even
pawns, but knights have a reputation for making especially vicious forks
because other pieces cannot block their way because the endangered
pieces cannot defend by attacking it, unless they are another knight.

### Forking with check

A knight fork that attacks the king from an unguarded square is very
powerful. The opponent must then move his king to safety and the other
piece in the fork has no chance of escape.

#### The Royal Fork

A *royal* fork is one involving both your opponent\'s king and queen. In
the example shown here, white\'s knight on f7 has engaged black in a
royal fork. Black will be down the exchange of a queen for a knight.


### Forks do not always win material

If every time you saw a fork you played it, you would be making a
mistake. You have to examine the different possibilities to escape the
fork. In the queen fork on the right white has just played 1.Qd4+
forking the black king and rook. However black can play 1. \...Rg7
blocking the check and moving the rook to safety (although white could
play 2.Qxg7, taking the rook, black could then play 2. \...Kxg7, taking
the queen; white will then have lost the Exchange and will be unable to
destroy Black\'s pawn majority, resulting in a forced win for Black, a
queened pawn, and a king-queen checkmate.)

However 1.Qd4 is by no means a bad move. Perhaps White played 1.Qd4 in
order to force black to play 1. \...Rg7 in which White can now play
2.Qd8+ (fork on king and pawn) Rg8 (forced) followed by 3.Qxa5 in which
case White can push his a-pawn. Here White forked Black\'s king and rook
not to win the rook but to later win a pawn by a fork, and pave the way
for his a-pawn to become promoted to a queen. He might have also
intended to play 3.Qf6+ Rg7 (forced) 4.Qxc6, eliminating Black\'s passed
pawn.

{{-}}

## Pinned pieces

A pinned piece is a piece that cannot move because it would expose an
attack on an important piece by one of the opposing pieces, such that
the capture of said piece would result in material gain by the opponent.
A great tactic is to pin the opponent\'s pieces to his king; this is
known as an *absolute pin*. For example, take a look at the board on the
right. Black just moved his dark-squared bishop to **b4**. The white
knight is now pinned and cannot move, because moving the knight would
put himself in check. White\'s only way to stop the pin is to move his
king. The pawn on **e4** is no longer guarded by the knight, since the
knight could not move to exchange.

The position diagrammed to the right shows the theme of attacking the
pinned piece. White can look at this position and immediately take the
rook and win an exchange. However this wouldn\'t even be the best move.
If white did this then the material would be dead even; however, white
has more pawn islands and it would be a very close game. Instead, white
can play Ng5! The rook cannot move, and black has no way of effectively
defending the rook a second time, therefore Black will eventually lose a
rook. So, if you have pinned a piece, try to see if you can attack the
piece again, and if a piece of yours is pinned, try to see if your
opponent can attack it again. The moral of the story: if you see a good
move, stop and look around for a better one.

In contrast to the absolute pin, a *relative pin* occurs when one
player\'s piece is pinned to one of lesser value than the king, such as
a queen or rook. If the benefit of moving the pinned piece outweighs the
loss of material occasioned by the capture of the exposed piece (for
example, if a forced mate may be achieved), then the pin can be
disregarded and the pinned piece moved.

{{-}}

## Skewers

A skewer is similar to a pin, but it is in a sense more powerful. The
difference between a pin and skewer is the location of the more
important piece. In a pin the lesser piece blocks the attack on the more
important one, in a skewer the more important piece is attacked first
and when it moves it exposes the lesser piece behind it to be hit. Black
has, in a blunderous moment, placed his king on **d7** in front of his
queen on **d8**. White may now triumphantly slide either rook to **d1**,
skewering Black\'s king and queen. Since Black cannot block the check,
the king has to move, exposing the black queen to the attack of the
white rook.

{{-}}

## Discoveries

A discovery is an attack on an enemy piece which is unveiled by moving
one of your pieces. The power of discoveries is that two targets can be
attacked simultaneously. If combined with a check they can be lethal.

{{-}}

Note that White\'s 1.Nd7+ was a *double check*, a type of discovered
check where the piece moving also gives check. Such checks are very
powerful, since the king is forced to move (both checks cannot be
blocked at the same time). They are also often lethal, as in the above
game. {{-}}

A simpler example of a discovered checkmate is shown below.


## Removing the defender

By first capturing, threatening, or pinning a piece that guards another,
you should be able to capture the other piece for free. You can also
remove the defender of a position. By using tactics you might be able to
force a checkmate!

## Sacrifices

A sacrifice is an exchange of a piece for a non material advantage:
    {{-}} In the first diagram, White just moved **1. Kh1**
to get out of check.

Black sacrifices his queen with **1\...Qg1+** for a winning positional
advantage - White is in check and can not take with his king because the
knight guards the queen.

**2. Rxg1** - forced - this smothers the king - he cannot move because
his own pieces are on every square he could go to - any check on an
unguarded square now is mate.

**2\...Nf2#** Checkmate. This queen\'s sacrifice was an example of a
smothered mate (in which a knight
delivers a checkmate that is caused by the king\'s inability to move
anywhere). In fact, this is a special kind of smothered mate, called
*Philidor\'s Legacy.*

{{-}}

## Zwischenzugs

A *Zwischenzug* (pronounced
\"TSVISH-en-tsoog\",) or \"in-between move,\" is one that is made
unexpectedly in the midst of a sequence of moves. But not just any
series of moves, one in which the player falling for the Zwischenzug
feels the sequence is forced, while his opponent demonstrates to him
that it certainly isn\'t! Most commonly these fall in between trades
where a recapture seems to be the only proper means of play.

Such in-between moves often have a surprising and pleasing effect of
increasing the potency of a combination beyond the opponent\'s
expectations.

In Borisenkov-Mezenev (shown in the diagram to the right), black played
**1\... f2**, threatening to queen, which White countered with **2.
Rg8**, intending **3. Rf8+**, and **4. Rxf1**. But White resigned after
the Zwischenzug **2\... Bb1!** which allows Black to queen (**3. Kxb1
f1=Q+** or **3. Rf8+ Bf5**).{{-}}


it:Scacchi/Tattica
