[A]ny tactical operation no matter how complex, can be described in terms of different combinations of contacts. ...to certain constellations of pawns, pieces or squares on the chess board.This week's lesson of the week includes only that for the beginning club. My advanced club does not meet this week due to the end of the first quarter and parent-teacher conferences. I introduced three terms that name relationships between the pieces--pin, fork, and skewer. Each was presented in a simple position where Black's pieces are vulnerable due to standing on the same rank. White's possession of a rook permits attacking both king and bishop in three different ways.
Yuri Averbakh, Chess Tactics for Advanced Players (1992)
The rook is able to move to the sixth rank between the bishop and king. The king must move out of check, then the rook can capture the bishop. This is called a fork because the rook attacks two pieces in different directions.
The rook again moves to the sixth rank, but this time in a manner that prevents the bishop from moving. The bishop is pinned against the king.
The rook moves to the sixth rank attacking the king with check. After the king moves, the bishop is exposed to the rook's hunger. The king is skewered like a piece of tofu ready for the grill.
After presenting these simple illustrations, I showed the students part of a game that I lost.
White to move
My opponent seized on the presence on my king and queen on the same file.
I threw away a knight in the futile effort to save the queen. Although it seemed like a good idea, White's additional tactics prevailed. This move was actually the game losing blunder.
I add a second rook to the one already pinning the knight.
29.cxb7+ Kxb7 30.Rxc7+ Kxc7 31.Qc3+ Kd6
White to move
The problem with my knight sacrifice is revealed. The queen now defends the knight. Of course, I could trade the two rooks for the queen and knight, a gain of material, but that would leave me in a hopeless king and pawn ending. The alternatives are even worse, however.
In this game fragment, we see elementary pins at work in a complex position. If the young student learns these patterns through simple diagrams like the three above, he or she will develop the ability to see such contacts in more complex positions.
*27.Rc3 was an error. Although it seems like a simple and correct move. I could have gained the advantage with 27...Ree1. White had a better move that maintains equality, a fork. Can you spot it?