In chess, a smothered mate is a delivered by a knight in which the mated king is unable to move because he is surrounded (or smothered) by his own pieces.
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 diagram to the right. 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 (see algebraic notation for an explanation of this notation). Similarly, white can be mated with his king on h1 and the knight on f2. Analogous mates on a1 and a8 are rarer, because king-side castling is more common than queen-side, and because after king-side castling the king is closer to the corner than it is after queen-side.
For a smothered mate of this sort to occur in a game, it is usually necessary to sacrifice material to compel pieces to smother the king - a player is unlikely to voluntarily surround his king with pieces in a position where a smothered mate is possible. One method is particularly common - an example is to be found in the game between Jan Timman (white) and Nigel Short (black) at the 1990 Tilburg tournament. From the diagrammed position, play continued 27.Nf7+ Kg8 28.Nh6+ Kh8 29.Qg8+ Rxg8 30.Nf7#. The procedure is: check with the knight, then move the knight away to deliver a discovered check from the queen, then sacrifice the queen to force the rook next to the king, then mate with the knight.
This technique is so common as to have its own name: Phildor's Mate or Philidor's Legacy (after François-André Danican Philidor). This is something of a misnomer, however, as it is first described in Luis Ramirez Lucena's 1497 text on chess, Repetición de Amores e Arte de Axedrez, which predates Philidor by several hundred years.
Occasionally, a smothered mate may be possible in the opening of a game. One particularly famous 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 to the right). Note that the knight cannot be taken because the bishop on e2 is pinnedned to the white king by the queen.
An example of a similar smothered mate in master-level play is the game between Edward Lasker (white) and Israel Horowitz (black) in 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#
