ChessA pin is attacking a piece that has a more important piece standing right behind it. If the front piece moves, the one behind gets taken, so it has to stay put. When you play chess against the computer, a lot of "how did I just lose a piece?" moments come from a pin you didn't notice.
What it looks like
Only pieces that move along lines can pin: rooks, bishops and queens. In this example, one rook move nails the black queen to the spot in front of her king.
The black queen can only move along the e-file, and anywhere she goes she's still in the rook's line of fire. If she takes the rook on e1, the white king takes her back from d2. A rook for a queen is a great deal for White.
Absolute pins and relative pins
Absolute pin: the king is behind
If the piece behind is the king, the pinned piece is not allowed to move by the rules, because moving would put its own king in check. That's an absolute pin.
That's the whole idea of the Nimzo-Indian Defense: the knight on c3 is pinned, so White has one less helper for pushing e4.
Relative pin: a queen or rook is behind
If the piece behind is something valuable like a queen or rook, the pinned piece can move, but moving loses the piece behind it. That's a relative pin.
Be careful with relative pins: sometimes giving up the piece behind gets you something even bigger. There's a famous trap in the Philidor Defense where White ignores the pin, gives away the queen, and ends up mating the black king.
A real example: smothered mate in the Caro-Kann
A pinned piece also can't protect other squares. This is the part many players miss:
The e7 pawn stands between the white queen and the black king. If it took the knight on d6, the e-file would open and the king would be attacked by the queen, so that move is illegal. The black king is surrounded by its own pieces, and that's checkmate. For the full story, see the Caro-Kann Defense.
How to defend
- Don't put your king and queen on the same line, especially an open file or diagonal. Enemy rooks and bishops will find them fast.
- Castle early. With the king tucked in the corner, it's much harder to get pinned on the central e-file.
- Break the pin early. Put another piece between the pinned piece and the one behind it, or move the piece behind out of the way first.
- Kick the pinning piece with a pawn. For example, if an enemy bishop on g4 or b4 is pinning your knight, think about h3 or a3 to ask whether it wants to trade.
Practice puzzles
Show answer
1. Bc4 The bishop goes to c4 and pins the black queen to her king. The queen can't leave that diagonal. If she takes the bishop, the b3 pawn takes back, and Black has given a queen for a bishop. Ouch.
Show answer
1. f4 Push the pawn to f4 and attack the knight. It's absolutely pinned, so it can't run. Even if the black king steps aside first, the pawn still takes the knight next move. Hitting a pinned piece with your cheapest pawn is the textbook way.
Show answer
1. Qxg6 The queen just takes the knight on g6! The f7 pawn is pinned to the king by the white bishop on c4, so it can't take back. A pinned piece can't protect anyone.
FAQ
What's the difference between a pin and a skewer?
Both involve two pieces on one line. In a pin, the front piece is worth less, so it doesn't dare move. A skewer is the opposite: the front piece is worth more (usually the king), so it has to move, and the piece behind gets taken.
What should I do when I'm pinned?
First check whether it's absolute or relative. In an absolute pin (king behind), that piece simply can't move, so look for a way to block or move your king. In a relative pin, do the math: sometimes moving away is worth it.
Can the king be pinned?
No. The king can never move to a square where it could be captured, so it never "stands in front" of another piece as a pinned piece. The pinned piece is always some other piece in front of the king.
Try it yourself
Pins and forks often show up together, so take another look at the fork, or see every tactic in chess tactics. Next time you play chess online, try using a bishop to pin an enemy knight to the queen or king.