In this part, we look at two related types of tactic, the pin and the skewer. A piece is pinned when it cannot move without exposing a more valuable piece to attack. A skewer is when a valuable piece is attacked, and when it moves, a lesser piece is exposed to capture. So, in a sense, the skewer is the inverse of the pin. Unlike forks, only the long range pieces - the bishop, rook and queen, are able to perform pins and skewers.
In case you still aren't clear, here is an example of a pin.
The black knight on f6 is pinned by the white bishop. If it were to move away, the white bishop would be able to capture the black queen, so we say that the knight is pinned to the queen. Pins are important tactical resources, because they allow us to severely restrict the mobility of the enemy pieces. A piece that is pinned can often be won by attacking it. Here is an example.
Another important feature of pins is that when a piece is pinned, it can no longer effectively defend other pieces. Sometimes a piece that appears to be doing an important job guarding a piece or square is actually unable to do a thing because it is pinned. This is especially the case when the piece is pinned to its king, as then it cannot move at all or it would expose the king to check. This is known as an absolute pin. Here is an example you should watch out for in your own games.
Pins can be very annoying when you're on the receiving end, as they can tie down your pieces and make it difficult for you to carry out your plans. The good news is that there are techniques for breaking out of a pin.
One way to get out of a pin (and many other difficult situations) is to give a check. Not just any old check - the idea is to give check with either your pinned piece or the piece it is pinned to. Then, when your opponent is dealing with the check you can move your other piece out of trouble as well. Here is an example:
Another way to break out of a pin is to put another piece in the way. You can place a piece between the enemy piece and the piece that is pinned, or in some cases, you can even put one between the pinned piece and the piece it is pinned to. Here are examples of each:
While a pin is a means of restricting the movement of an enemy piece, a skewer usually results in the outright capture of one. Here are some examples.
Skewers can sometimes be broken by the same methods as pins, mentioned above, but it is usually best to avoid having your pieces skewered if at all possible. Having several unprotected pieces in a line is usually a danger sign for a potential skewer. If you place two rooks on the same diagonal, you should always look out for any possibility of them being skewered by an enemy bishop. Likewise, two bishops or knights on the same rank or file are vulnerable to being skewered by a rook or queen. Especially be aware of any pieces that could be skewered along the same line as your king.
Here's your chance to test your knowledge of pins and skewers. On each of the boards below, try to find the move which will best take advantage of a pin or skewer.