Smothered mate

In chess, a smothered mate is a checkmate delivered by a knight in which the mated king is unable to move because he is surrounded (or "smothered") by his own pieces. In rare situations, the surrounding pieces may include an opponent's defended piece, which the king can not capture.
The mate is usually seen in a corner of the board, since fewer pieces are needed to surround the king there. The most common form of smothered mate is seen in the adjacent diagram. The knight on f7 delivers mate to the king on h8 which is prevented from escaping the check by the rook on g8 and the pawns on g7 and h7. Similarly, White can be mated with the white king on h1 and the knight on f2. Analogous mates on a1 and a8 are rarer, because castling is more common than castling and brings the king closer to the corner.
Introduction.
For a smothered mate of this sort to occur in a game, it is usually necessary to sacrifice to compel pieces to smother the king – a player is unlikely to voluntarily surround their king with pieces in a way that makes a smothered mate possible. One method is particularly common and involves: a check with the knight forcing the king to the corner of the board, then moving the knight away to deliver a double check from the queen and knight, then sacrificing the queen to force the rook next to the king, then mating with the knight. 
An example is to be found in the game Jan Timman–Nigel Short at the 1990 Tilburg tournament. From the diagrammed position, play continued 27. Nf7+ Kg8 28. Nh6++ Kh8 29. Qg8+ Rxg8 30. Nf7#. (Note that White would force mate even if his rook, and pawn on e7, were removed from the board, and Black had a knight on f6. In that case, 27.Nf7+ Kg8 28.Nh6++ Kh8 (28...Kf8 29.Qf7#) 29.Qg8+! Nxg8 (or 29...Rxg8) 30.Nf7 still mates.) This technique is so common as to have its own name: "Philidor's Mate" or "Philidor's Legacy" (after François-André Danican Philidor). This is something of a misnomer, however, as it is earlier described in Luis Ramirez Lucena's 1497 text on chess, "Repetición de Amores e Arte de Axedrez", which predates Philidor by several hundred years.
In the opening.
Occasionally, a smothered mate may be possible in the opening of a game. One of the most famous, and most frequently occurring, is in the Budapest Gambit. It arises after 1. d4 Nf6 2. c4 e5 3. dxe5 Ng4 4. Bf4 Nc6 5. Nf3 Bb4+ 6. Nbd2 Qe7 7. a3 Ngxe5 8. axb4?? Nd3# (final position at left). Note that the knight cannot be taken because the pawn on e2 is pinned to the white king by the black queen on e7. 
Another notorious example is the so-called "Blackburne Shilling Gambit" (named after the 19th century English player Joseph Henry Blackburne, supposedly because he used it to win shillings from amateurs). It goes: 1. e4 e5 2. Nf3 Nc6 3. Bc4 Nd4?! 4. Nxe5!? Qg5! 5. Nxf7?? Qxg2 6. Rf1 Qxe4+ 7. Be2 Nf3# (final position at right). There is also a well-known trap in the Caro–Kann Defence: 1. e4 c6 2. d4 d5 3. Nc3 dxe4 4. Nxe4 Nd7 5. Qe2!? Ngf6?? 6. Nd6#. This trap has claimed many victims, perhaps the earliest recorded example being Alekhine–Four Amateurs, simultaneous exhibition, Palma de Mallorca 1935.
Examples from games.
An example of a similar smothered mate in master-level play is the game Edward Lasker–Israel Horowitz, New York City 1946, which went: 1. d4 Nf6 2. Nf3 d5 3. e3 c5 4. c4 cxd4 5. Nxd4 e5 6. Nf3 Nc6 7. Nc3 d4 8. exd4 exd4 9. Nb5 Bb4+ 10. Bd2 0-0 11. Bxb4 Nxb4 12. Nbxd4 Qa5 13. Nd2 Qe5+ 14. Ne2 Nd3#.
Another example is the game Unzicker–Sarapu, Siegen Olympiad 1970: 1. e4 c5 2. Nf3 Nf6 3. e5 Nd5 4. Nc3 e6 5. Nxd5 exd5 6. d4 Nc6 7. dxc5 Bxc5 8. Qxd5 Qb6 9. Bc4 Bxf2+ 10. Ke2 0-0 11. Rf1 Bc5 12. Ng5 Nd4+ 13. Kd1 Ne6 14. Ne4 d6 15. exd6 Bxd6?? 16. Nxd6 Rd8 17. Bf4! Nxf4? 18. Qxf7+ Kh8 19. Qg8+! Sarapu now resigned in light of 19...Rxg8 20.Nf7#.
References.
Bibliography