The pin

A game on lichess.org, 2014, move ten. The white queen stands on e4 and checks the black king on e8. The queen is in plain view, the black bishop on f5 attacks it, but White is calm: the knight on c3 defends e4. If the bishop takes the queen, the knight takes the bishop.

But there is something behind the knight. A black bishop stands on b4, and between it and the white king on e1 there is only the knight on c3. If the knight leaves c3, the king is in check, and you may not put your own king in check. The knight only seems to defend e4. Find Black's move.

White did not blunder the queen in the usual sense: they counted the defender. They did not check whether it was free to move. This mistake happens at every level and costs a lot, a queen or a rook, yet you can see it in a second once you know where to look.

In the last chapter a fork attacked two targets, and the opponent saved one. Here there was nothing to save: the defender could not move. Such a piece is called pinned, and that is what this chapter is about.

What a pin is

A pin happens when a piece stands on a line along which an enemy rook, bishop or queen strikes, and shields something valuable behind it. If it moves away, the blow lands on what is behind it. Only long-range pieces pin: a knight or a pawn hits a single square and shields nothing.

Every pin has three parties. The pinning piece is the opponent's rook, bishop or queen. The pinned piece stands first on its line. Behind it, on the same line, stands what it shields: the king, the queen, a rook or just an undefended piece. Remove any of the three and the pin is gone. That is why the ways of fighting a pin, which we come to at the end of the chapter, are all ways of removing one of the parties.

Pins come in two kinds, and the difference between them is huge.

• A pin to the king (called an absolute pin). The rules forbid the pinned piece to move: the king may not be left in check, as you remember from chapter 5. At most the piece can slide along the same line without exposing the king.
• A pin to the queen, a rook or another valuable piece (a relative pin). The piece may move, the rules allow it. But the move costs whatever stands behind it. Sometimes it is worth it: in chapter 10, in Légal's Mate, White moved a pinned knight, gave up the queen and mated.

Here is the best-known pin in the opening. After 1. e4 e5 2. Nf3 Nc6 3. Bb5 d6 in the Ruy Lopez, the black knight on c6 finds itself between the bishop on b5 and the king on e8: the pawn on d7 has moved and opened the diagonal.

The move 3. Bb5 is not played for the pin: the bishop attacks the knight on c6, and the knight defends the pawn on e5. While the pawn stays on d7, nothing holds the knight. But as soon as Black plays …d6 or …d5, the bishop on b5 starts looking through the knight at the king. Many openings work the same way: a bishop comes out onto a line where an enemy piece has the king or the queen behind it, and waits for the pin to take effect.

A pin to the queen looks the same, but the rules do not help it. Tell them apart on one board.

The pinned defender

The most common consequence of a pin is the one the chapter began with. The pinned piece seems to defend the squares around it, but it cannot capture on them. Before you count defenders, check that they are free. Below are five positions from real games, and in each one a defender is pinned. Sometimes it is a knight, sometimes a pawn or a bishop, sometimes the pin runs along a file.

The habit you need here is simple. When you count a piece's defenders, ask of each one: what stands behind it on the line of an enemy rook, bishop or queen? If it is the king, that defender does not count. If it is the queen, it counts only if you are ready to give up the queen. Strong players run this check without thinking, and for them such positions are simply a free queen.

A pinned defender does not always give a piece away for nothing. Sometimes the attacked piece has two defenders, and only one of them is pinned. Then the capture is a trade, but a good one: you give less than you take.

Count again, as in this puzzle: the queen has two defenders, but only the pawn on f3 counts. Black gives a knight for the queen, and the pinned defender turns a trade into a win.

A pawn can be pinned too, right next to its own king. The pawn on f7 in front of a castled black king is a frequent victim: once a white bishop stands on the c4–g8 diagonal, the pawn on f7 no longer defends anything.

Attacking the pinned piece

A piece pinned to the king cannot run away, so you attack it again, and best of all with a cheap piece, a pawn. If the pinned piece is defended only by a pawn and you attack it with a pawn, you trade a pawn for a piece. If nothing defends it, the piece is lost for nothing.

You can attack with other pieces too. If more of your pieces attack the pinned piece than defend it, it is lost: it cannot leave, and you take it when it suits you. This is called piling up on the pin. The defending side tries to add defenders in reply, or to break the pin altogether before it is too late.

A pin does not only run along a diagonal. A rook on an open file pins everything that stands between it and the king.

Next to this rule stands a warning. A piece pinned to the king may move along the line of the pin itself if it does not expose the king: a rook pinned along a file may move along that file, and a bishop pinned along a diagonal may move along the diagonal. So it may also take the piece that pins it, if it can reach it.

A knight cannot do this: every move takes it off the line. A pawn almost cannot: pinned along a file it may go forward, and pinned along a diagonal it may only take the pinning piece, if that piece stands right next to it. A pinned knight is the most helpless piece on the board. That is why experienced players are so fond of pinning knights.

Setting up a pin

To pin a piece, put a long-range piece on a line where the enemy piece has the king or the queen behind it. It is best when the pinning piece cannot be taken, or when taking it costs the opponent more.

Where do you look for such lines? A king that has not castled stands on the e-file and on the a4–e8 and h5–e8 diagonals (for White, a5–e1 and h4–e1). Anything that comes onto these lines in front of the king is a candidate for a pin. Early in the game the queen stands on d8 or d1, and a bishop on g5 or b5 (for Black, on g4 or b4) pins a knight to the queen or the king. In the endgame a rook pins an enemy rook that stands on the same rank or file as its king.

You can also set up a pin in reply to a check, by taking the checking piece. Then the opponent often loses even more than they bargained for.

Here the pin came with tempo. Taking the knight was the answer to a check, a move Black would have made anyway. The best pins are born this way: a piece comes onto the line for a reason, with a capture or a check, and pins along the way. The opponent has no time to prepare, because they are busy with their king.

A pin to the queen

A pin to the queen does not forbid the move, so people go wrong with it more often. The piece moves, and the player forgets what was behind it. See what the engine says about such a move.

The bishop on g5 takes the queen on d8, the rook takes the bishop, and after Bxd8 Rxd8 Black has given the queen for a bishop. A move with a pinned piece pays off only if it gains more than what stands behind it is worth: mate, as in Légal's Mate, or an even more valuable piece.

The best-known pin to the queen comes in the first few moves: a black bishop comes out to g4 and pins the white knight on f3 to the queen on d1, as in chapter 10. A knight move there is legal, but usually bad. White often replies h3, attacking the bishop: the bishop either trades itself for the knight or drops back to h5 and keeps pinning. You will meet this argument over the pin in many of the openings in part three.

How to get out

If one of your pieces is pinned, you cannot wait: the opponent will bring up fresh forces and attack it again. There are four ways out.

1. Move what is behind. Take the queen off the line or, if the pin is to the king, step away with the king. Then the piece is free.
2. Block. Put another piece between the pinned piece and the valuable one. The pinned piece is freed, though another piece now stands on the line. In the Ruy Lopez after …d6 Black often does just that: …Bd7 puts the bishop between the knight on c6 and the king on e8, and the knight can move again.
3. Attack the pinning piece. Most often with a pawn: the moves h6 and a6 against a bishop on g5 or b5 are called "asking the bishop". The bishop has to either trade itself for the pinned piece or retreat and perhaps let it go.
4. Trade or capture. If you can take the pinning piece, or give something equal for it, the pin disappears.

Every way out costs something. Stepping away with the king loses time, and sometimes the right to castle. Blocking puts one more piece on the line, and that piece is now pinned itself, if only to something less valuable. The moves h6 and g5 against a bishop on g5 free the knight but open up your own king's position if it has castled on that side. Choose the way out that costs least in the position in front of you. And remember that the best moment to break a pin is before the opponent has started piling up on it.

What's next

In a pin the valuable piece stands behind and hides behind a less valuable one. What if it is the other way round? The valuable piece stands in front, it is attacked, it moves away, and the blow lands on what was behind it. That is the skewer. And when a long-range piece strikes through an enemy piece at the square behind it, people speak of an "X-ray". The next chapter is about both. The lines there are the same as in the pin, and so is the check: what stands behind a piece on the line of a rook, bishop or queen. Only the order changes: who is in front and who is behind.