A skewer occurs when a valuable attacked piece must move (to save itself) and thus exposes a piece of lesser value to attack and capture. Skewers occur less often than forks and pins, especially in short games, but when they do they are often decisive. Whenever two pieces are lined up on a rank, file, or diagonal, look for a pin or a skewer.
The position at left is from the game Salov vs. Polgar (1997). Black won the game using a skewer as follows: 1...Rb1 Black threatens 2...Ra1++. White cannot move the rook; the king must be moved instead to avoid checkmate. 2. Ka5 (or Ka3, it doesn't matter) 2...Ra1+ The king is skewered. It must now move out of the way exposing the black rook behind it to capture. 3. K moves Rxa8 and wins.
The position at right is from the game Short vs. Vaganyan (Barcelona, 1989). White picked off black's queen by 1. Be5+ Black resigned rather than watch 1...Kxe5 2. Qc3+ K moves 3. Qxg7. Skewered again! Notice in this case the skewer had to be set up by a bishop sacrifice. 1. Qc3+ would have done no good, as the black king could have moved to a square where it protects the black queen. The bishop sac pulled the black king far enough away from the queen that the skewer would work.
Skewers do not have to involve the king. Here is one from a master game (players not given). The position is from Chernev and Reinfeld's book Winning Chess, an excellent source of practice problems on tactics, both elementary and advanced. Black plays 1...Nxc4 If white recaptures, his queen and rook become lined up on the same diagonal, a situation ripe for a skewer. 2. Qxc4 Be6 Black executes the skewer. 3. Qe2 (Why here?) 3...Bxa2 and black has won the exchange.
Here is my favorite game involving all three of the basic tactics we've discussed. This was a tournament game I played many years ago in a double round robin tournament. That is a tournament in which each participant faces every other participant twice, and this was my second game against Randy (who up until this game was undefeated and untied in the tournament). He had beaten me rather badly in our first game, so I was out to even the score. The game is almost all tactics. See if you can anticipate them.
Randy Roehll vs. Bill King (Ohio State Univ., 1972) 1. e4 e5 2. Nc3 Nf6 3. Bc4 Nxe4 Have I lost my mind? It looks like I'm giving away a knight. In fact, it is protected by the threat of a pawn fork. If 4. Nxe4 d5 picks up either the white knight or the white bishop. 4. Qh5 This is also a fork. The white queen threatens the undefended e5 pawn, and also threatens to take on f7 with checkmate. Can black defend against both threats at once? 4...Nd6 Not really. But white is after an attack and is not all that concerned with reclaiming his pawn right now. If 5. Qxe5+ Qe7 and the queens will be traded, taking all the sting out of the position. 5. Bb3 Nc6 Black defends the e5 pawn and develops a piece. 6. Nb5 At first this appears to be an amateur move, moving the same piece twice in the opening, and removing it from influencing the center, but these are special circumstances. Do you see how white has renewed the mate threat on f7? If white can knock out the d6 knight, black will once again be vulnerable to checkmate. Black needs to do something about that right now. 6...g6 7. Qf3 The threat on f7 still exists. Black needs to find another defense. 7...f5 8. Qd5 Again white renews the threat on f7. Black must now defend with his queen, and that leaves me vulnerable to a knight fork. Do you see it coming? 8...Qe7 9. Nxc7+ Randy has not only won his pawn back but has a fork on the black king and rook to boot. This is the point of all his maneuvering with the knight and queen. 9...Kd8 10. Nxa8 b6 White has gone up a rook. In fact, he's not getting that knight out of the corner safely so, in effect, white has won the exchange. What did black get in compensation for his material loss? 11. d3 Bb7 12. h4 Now what is Randy's threat? Black's king and queen are lined up like ducks in a row, so the threat is 13. Bg5 with a deadly pin that would win black's queen. 12...f4 13. Qf3 Nd4 There are forks and threatened forks all over the place! First, the black bishop on b7 forks the white knight and queen. Second, the black knight on d4 forks the white bishop and queen. Third, should the white bishop remove its defense from c2 (by moving to d5, for example), black has a knight fork on c2. Black is behind in material, but his pieces are very active and it is black that is now on the attack (has the initiative). It may surprise you to learn that this is a well known opening. Up until here, both Randy and I have been playing "a book opening" called the Vienna Game. 14. Qg4 Bxa8 This was probably a waste of time. The white knight wasn't going anywhere, and black's hopes lie in a quick kill. I should have pressed the attack here. 15. Qg5 White's hopes, on the other hand, lie in quieting the position down, blunting black's attack, and getting some material off the board so that his material advantage will weigh more heavily in the balance. He has pinned black's queen to the black king. Randy was calculating that the exchange of queens would substantially dull my attacking chances. 15...N6f5 16. Nh3 There is no hurry to trade queens. The black queen is still pinned and isn't about to run off to join the fight. Still, this move was a mistake. Do you see how it leaves white's h4 pawn vulnerable. This is sometimes called an x-ray attack--a version of the skewer--because the force of the black queen shines right through the white queen and hits the pawn on h4. Before white's knight move, this pawn was also protected by the rook, but now it no longer is. 16...Nxh4 Black has not only won a pawn but has a dastardly threatened fork. Do you see it? If white isn't careful, he will face 17...Nhf3+ 18. gxf3 Ndf3+ with a fork on the white king and queen. White decides to trade queens to eliminate this threat and calm the position down. 17. Qxe7+ Bxe7 18. f3 Nxg2+ 19. Kf2 Bh4+ Black brings another piece into the attack. How is the black knight defended? 20. Kxg2 Bxf3+ The white king is skewered. 21. Kh2 Bg3+ 22. Kg1 Ne2+ The knight forks the white king and bishop, but more to the point black is trying to drive the white king away from his rook so the rook can be snatched up for free. 23. Kf1 Nxc1 24. Ng5 A peculiar fork in which the white knight attacks both the black bishop on f3 and the f7 square. If the white kinght gets to f7, it will be forking the black king and rook. It's a weak defense, but I don't think Randy was up to his usual high standard on this evening. 24...Bxh1 The skewer finally nets the white rook. 25. Nf7+ And white makes good on his threatened fork. 25...Ke7 26. Nxh8 Nxb3 27. axb3 a5 28. b4 f3 White is done for. His knight is trapped in the corner, and black has a dangerous passed pawn. 29. bxa5 Bg2+ 30. Kg1 bxa5 31. Rxa5 Bh3 and white resigned. White will have to give up his rook to stop the passed pawn from promoting: 32. Ra1 f2+ 33. Kh8 f1=Q+ 34. Rxf1 Bxf1 and white is wiped off the board.
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