Skewer

A skewer is a pin turned inside out. Two enemy pieces sit on the same line, one attacked piece is more valuable and stands in front, and a less valuable piece sits behind it. Instead of freezing the front piece the way a pin does, a skewer forces it to move — usually because it's in check — and whatever was hiding behind it is left exposed to be won.

What actually separates a skewer from a pin

The two tactics look almost identical on the board — an attacker, a line, two enemy pieces on it — and the only real difference is which piece is closer to the attacker. In a pin, the LESS valuable piece is in front and the more valuable piece is pinned behind it; the front piece is stuck. In a skewer, the MORE valuable piece is in front, and because it has to move (most often because the position is check), the piece behind it is left hanging. That ordering is everything: a bishop attacking a knight with a rook hiding behind it is a pin on the knight, but a bishop attacking a rook with a knight hiding behind it is a skewer on the rook.

Why the king shows up in so many skewers

The king is the single most common front piece in a skewer, for a simple reason: a king in check has no choice but to move (or block or capture, when those are available), while every other piece could in principle just sit still and accept the loss behind it. That's why a rook or queen delivering a long-range check is worth a second look even when it doesn't look like it wins anything immediately — the real question isn't "is this check good," it's "what happens to be standing on the same line behind the king once it's forced to move." A check that looks like a routine spite check can turn out to be a full piece.

Finding skewers by working backward from the king

Rather than scanning randomly for skewers, look at where the enemy king sits and ask which of your long-range pieces could reach a square on the same rank, file, or diagonal as the king, with something valuable of the opponent's parked further along that same line. Open files and long diagonals that run through the enemy king are worth checking on every move, even moves that don't look tactical, because the opponent's own pieces tend to line up on them without realizing it — especially a queen that has retreated to the back rank for safety, which is exactly the kind of piece a skewer loves to find.

Defending against a skewer

Because skewers usually arrive with check, the defensive options are the normal check-response options: block the line if a piece can reach it, capture the attacker if possible, or move the king somewhere that doesn't leave the second piece on the same line at all. The last option is the one players miss — when responding to check, it's worth checking two things at once: is this square safe, and does it also get my other piece off this attacker's line? Moving the king to a square that's technically legal but still leaves the queen or rook lined up behind it on a different square of the same diagonal solves nothing.

The mistake of confusing a skewer with a simple check

It's easy to play a check purely to gain a tempo or push the king somewhere slightly worse, and completely miss that the same check also skewers a piece behind it — the two ideas (harassing the king, and winning material through it) can look identical until you specifically check what's on the line beyond the king. Conversely, it's just as easy to see the material win and miss that the king actually has a legal in-between move — a capture, an interposition, or occasionally a counter-check — that escapes with everything intact. Always verify the front piece truly has no other option before counting the material as won.

A skewer and a pin are close enough relatives that it's worth deciding which one you're actually looking at before calculating further — the follow-up technique for each is different, and treating a skewer like a pin (piling up extra attackers instead of just taking what's exposed) wastes moves you don't need to spend.