The junior chess club started on 04/10/10. Five boys turned up to enjoy some chess. The main idea is to lean by playing, but with the focus on fun. Each week I will discuss a tactic. The first week I explained the pin.
"The Pin is an attack against two or more hostile forces standing on a straight line (file, rank or diagonal). It is the most common, the most dangerous and hence the most important tactical weapon in the whole arsenal of combinations." Irving Chernev and Fred Reinfeld, Winning Chess
Below the white rook pins the knight to its king. It doesn't matter who is to move, as white's next will be rook take knight.
Below we see the bishop pinning a rook. Even though a rook (5) is worth more than a bishop(3) it is the bishop who will take the rook next move.
Last but not lease we see the queen pinning the rook on a diagonal and the bishop vertically. You may notice the bishop could move if it wanted, as queen takes rook is withing the rules. The pinned rook can not move as it is pinned to the king, it is illegal to move into check.
When a piece is pinned to its king then that is an absolute pin, or unbreakable pin, as the piece simply can not move. Other pins are not absolute which means the pinned piece can move, although in most cases moving a pinned piece would lead to losing material they are some cases where a pinned piece can wreck havoc, be warned!
Take a look at the following if you think the above positions too simple, this diagram is from the game N.Rossolimo C.Kottnauer, Bad Gastein 1948.
Did you spot 1. Qxd5
The bishop pins the c6 pawn to the king and the rook pins the e6 pawn to the king stopping pawn takes queen in both cases. To complete the pin hat-trick the queen also pins the c6 pawn to the rook (pins don't have to be against the enemy king) stopping cxb5.
I told you pins are dangerous