FEN = 6k1/6p1/p4Q1p/1p1P1b2/8/1P4RP/PBr3PK/4q3 w - - 0 1
When a piece is attacked and it cannot move without exposing a piece behind it to attack, the first piece is pinned to the piece behind it.
Remeber that it is legal to move the piece. Although when the piece is pinned to the King, the pinned piece can move only along the line of attack.To remove the pin (or "break" the pin), there are four basic ways:
1.1 Capture the pinning piece
FEN = 6k1/6p1/p4Q1p/1p1P1b2/8/1P4RP/PBr3PK/4q3 w - - 0 1
The g-pawn cannot capture the Queen on f6, as it is pinned by the Rook on g3.
Black to move. The answer is on the next page.
FEN = 6k1/6p1/p4Q1p/1p1P1b2/8/1P4RP/PBr3PK/4q3 w - - 0 1
One usual way to escape is to take the pinning piece, usually involving a sacrifice. But then
the pinned piece could make up for it with a capture when freed.
Another method is a double attack to the King and to the pinning piece, to capture it a move later.
1. ... 
xg3+! 2. 
xg3 gxf6
7r/2pR1bkp/1r6/p1N2qp1/P1QP4/2P5/5PPP/4R1K1 w - - 0 1
Black to move. The answer is on the next page.
7r/2pR1bkp/1r6/p1N2qp1/P1QP4/2P5/5PPP/4R1K1 w - - 0 1
1. ... xd7! 2. 
xd7 
xc4
1.2Attack the pinning piece
FEN = rn1qkbnr/ppp2ppp/3p4/4p3/4P1b1/3P1N2/PPP2PPP/RNBQKB1R w KQkq - 0 1
1. h3 putting the question to the pinning piece, but weakening the castle. The Bishop could trade the Knight, or move to e6 or move to h5 maintaining the pin.
White could try another way to break the pin, or attack again with g4, weakening more the castle. DON'T YOU DARE
See what it can happen to you:
1. e4 e5 2. f3 c6 3. b5 f6 4. c3 a6 5. xc6 dxc6 6. O-O g4 7. h3 h5 8.
g4 xg4 9. hxg4 xg4 10. g2 f6 11. d3 h5 12. 
h1 h4 13. h3 g5 14. h1 g8
15. e1 xh3+ 16. xh3 g4 17. h1 h3+ 18. g3 c5 19. e3 h8 20. d1 xe3 21.
fxe3 h4+ 22. h2 g3+ 23. g1 O-O-O 24. f3 dg8 25. f5+ b8 26. f1 h2 27.
e2 h1= 28. d2 4h2+ 29. c3 xe1+ 30. b3 g2 31. xf7 g1= 32. c4 gg2 33.
d4 exd4 34. b1 xe4 35. a4 b5 36. axb5 cxb5 37. c3 exc2+ 38. a3 bxc4 39. b3
a2+ 40. b4 xc3+ 41. c5 d6# 0-1
F Leveille 2360 vs. G Sagalchik 2515, Montreal, 1995.
This game can be seen here: attack http://scacchi.vecchilibri.eu/partite/attack.html .
1.3 Interpose
C50 Hungarian defence and Giuoco pianissimo
FEN = r2qkbnr/ppp2ppp/2np4/4p3/2B1P1b1/5N2/PPPP1PPP/RNBQ1RK1 w kq - 0 5
1. e2 while not always the best move available, seems to almost never be a bad move.
1.4 Get out of the way
C62 Ruy Lopez Steiniz Defence
FEN = rn1qkbnr/ppp2ppp/3p4/4p3/4P1b1/3P1N2/PPP2PPP/RNBQKB1R w KQkq - 0 1
Simply moving the Queen out of the way simply results in capture and double pawns, not a good idea.Therefore, before moving the Queen, protect the Knight in some way.
1. e4 e5 2. f3 c6 3. d4 d6 4. b5 g4 5. d3.
4q1k1/2p4p/1pn1p1p1/pB1pPp2/3P1P2/2P5/PP4PP/3Q2K1 w - - 0 1
Black to move, on next move White will play Qa4 to get the Knight. The answer is on the next page.
4q1k1/2p4p/1pn1p1p1/pB1pPp2/3P1P2/2P5/PP4PP/3Q2K1 w - - 0 1
1. ... a8! 2. a4 e7
Black's Queen gets out of the way, in the meantime protects the pinned Knight, that no more pinned can move away on the next move.
All the books about tactics will tell you the importance of pinning, and the way to take advantage by attacking the pinned piece withe a piece of yours of lower value.
Few will show you the technique to unpin without or with few damages.
The best way is to create a greater threat, capturing with one of your two pieces an opponent's piece, much better
with check to the King at the same time.
When this is not possible in the above diagram, with the danger if you move away one of the two pieces to
lose the other, what will you do? The answer is on the next page.
The Rook cannot move from the file to protect the Bishop or the Knight, but by simply losing one tempo, it can move to a square on the same file where it could be supported by the minor piece on the next move.
FEN = 3R4/1p3kpp/8/1P1b4/8/5N2/5KPP/3r4 b - - 7 31
Your move? The answer is on the next page.
FEN = 3R4/1p3kpp/8/1P1b4/8/5N2/5KPP/3r4 b - - 7 31
xf3! The Bishop captures the Knight, protecting his Rook at the same time. One piece up, as if gxf3 then xd8.
From the game Lajos Asztalos vs. Bjorn Nielsen, Munich, 1936.08.21.
Potete vedere questa e qualche partita di esempio e scaricare il pgn su: Unpinning http://scacchi.vecchilibri.eu/partite/unpinning.html . More than 20 examples.
Questa lezione è tratta dall'ebook disponibile su Amazon Learn how to unpin, che illustra completamente i metodi per schiodarsi, con vantaggio. http://www.amazon.it/dp//B0741XZG33