King's Gambit

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King's Knight's Gambit: 3.Nf3

This is the most popular move. It develops the knight and prevents 3...Qh4+. Black's two main approaches are to attempt to hold on to the pawn with ...g5, or to return the pawn in order to facilitate development.

The Classical Variation arises after 3.Nf3 g5. Black defends their extra pawn, and threatens to kick the f3-knight with ...g4. The main continuations traditionally have been 4.h4 (the Paris Attack), and 4.Bc4. More recently, 4.Nc3 (the Quaade Gambit or Quaade Attack[15]) has been recommended by Scottish grandmaster John Shaw as a less explored alternative to 4.h4 (he considers 4.Bc4 inferior).[16]

The Kieseritzky Gambit, 4.h4 g4 5.Ne5, is considered by modern writers such as Shaw and Gallagher to be the main line after 3...g5. It was popularized by Lionel Kieseritzky in the 1840s and used successfully by Wilhelm Steinitz. Boris Spassky used it to beat Bobby Fischer in a famous game at Mar del Plata in 1960.[17] The main line of the Kieseritzky Gambit is considered to be 5...Nf6 6.Bc4 d5 7.exd5 Bd6 8.d4 with an unclear position.

4.h4 g4 5.Ng5 is the Allgaier Gambit,[18] intending 5...h6 6.Nxf7. This knight sacrifice is considered unsound.[19]

The extremely sharp Muzio Gambit[20] arises after 4.Bc4 g4 5.0-0 gxf3 6.Qxf3, where White has sacrificed a knight but has three pieces bearing down on f7.[21] Such wild play is rare in modern chess, but Black must defend accurately. Perhaps the sharpest continuation is the Double Muzio after 6...Qf6 7.e5 Qxe5 8.Bxf7+!?, leaving White two pieces down in eight moves, but with a position that some masters consider to be equal.[22][23] In practice White's play seems to be easier, especially when the opponent is surprised by such daring tactics.

Similar lines are the Ghulam Kassim Gambit, 4.Bc4 g4 5.d4, and the McDonnell Gambit, 4.Bc4 g4 5.Nc3. These are generally considered inferior to the Muzio, which has the advantage of reinforcing White's attack along the f-file. Also inferior is the Lolli Gambit 4.Bc4 g4 5.Bxf7+?!, which leaves White with insufficient compensation for the piece after 5...Kxf7 6.Ne5+ Ke8 7.Qxg4 Nf6 8.Qxf4 d6.

The Salvio Gambit, 4.Bc4 g4 5.Ne5 Qh4+ 6.Kf1, is considered better for Black due to the insecurity of White's king. Black may play safely with 6...Nh6, or counter-sacrifice with 6...f3 or 6...Nc6.

A safer alternative to 4...g4 is 4...Bg7, which usually leads to the Hanstein Gambit after 5.d4 d6 6.0-0 h6 or the Philidor Gambit after 5.h4 h6 6.d4 d6 (other move orders are possible in both cases).

The Quaade Gambit (3.Nf3 g5 4.Nc3) is named after a Danish amateur who discussed it in correspondence with the Deutsche Schachzeitung in the 1880s.[24] The move has received renewed attention following its recommendation by John Shaw in his 2013 book on the King's Gambit. A well-known trap here is 4...g4 5.Ne5 Qh4+ 6.g3 fxg3 7.Qxg4 g2+? (7...Qxg4 8.Nxg4 d5 is about equal) 8.Qxh4 gxh1=Q 9.Qh5! and White is close to winning. (Black's best defense is considered to be 9...Nh6 10.d4 d6 11.Bxh6 dxe5 12.Qxe5+ Be6 13.Qxh8 Nd7 14.Bxf8 0-0-0 and White will emerge a clear pawn ahead.) Instead, 4...Bg7 has been recommended. 4...d6 and 4...h6 transpose to Fischer's Defense and Becker's Defense, respectively. Also possible is 4...Nc6, recommended by Konstantin Sakaev.[25][26]

After 4...Bg7 5.d4 g4, Simon Williams advocates 6.Bxf4 gxf3 in his DVD and Chess.com video series.[27] White is down a knight, but has a strong attack. The Quaade Gambit has recently been advocated by Daniel King in his PowerPlay series for Chessbase.

This is likely to lead to similar positions to the Quaade Gambit, however 4...g4 5.Ne5 Qh4+ 6.g3 fxg3 7.Qxg4 g2+!? (7...Qxg4=) is now viable due to the threat against the pawn on e4. After 8.Qxh4 gxh1=Q Shaw recommends 9.Nc3 for White, with a complicated position.[28]

The Becker Defense (3.Nf3 h6), has the idea of creating a pawn chain on h6, g5, f4 to defend the f4 pawn while avoiding the Kieseritzky Gambit, so Black will not be forced to play ...g4 when White plays to undermine the chain with h4. White has the option of 4.b3, although the main line continues with 4.d4 g5 (ECO C37) and usually transposes to lines of the Classical Variation after 5.Bc4 Bg7 6.0-0 (ECO C38).

The rarely seen Bonch-Osmolovsky Defense[29] (3.Nf3 Ne7) aims to defend the f4-pawn with ...Ng6, a relatively safe square for the knight compared to the Schallopp Defense. It was played by Mark Bluvshtein to defeat former world title finalist Nigel Short at Montreal 2007,[30] even though it has never been highly regarded by theory.

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Sample position in the Cunningham Defense

The Cunningham Defense (3.Nf3 Be7) threatens a check on h4 that can permanently prevent White from castling; furthermore, if White does not develop their king's bishop immediately, they would be forced to play Ke2, which hems the bishop in. A sample line is 4.Nc3 Bh4+ 5.Ke2 d5 6.Nxd5 Nf6 7.Nxf6+ Qxf6 8.d4 Bg4 9.Qd2 (diagram). White has strong central control with pawns on d4 and e4, while Black is relying on the white king's discomfort to compensate.

To avoid having to play Ke2, 4.Bc4 is White's most popular response.[31] Black can play 4...Bh4+ anyway, forcing 5.Kf1 (or else the wild Bertin Gambit or Three Pawns' Gambit, 5.g3 fxg3 6.0-0 gxh2+ 7.Kh1, played in the nineteenth century). In modern practice, it is more common for Black to simply develop instead with 4...Nf6 5.e5 Ng4, known as the Modern Cunningham.

The Schallopp Defense (3.Nf3 Nf6) is usually played with the intention of holding on to the pawn after 4.e5 Nh5. While it is not Black's most popular option, it attracted some attention in 2020 when Ding Liren used it to beat Magnus Carlsen in the online Magnus Carlsen Invitational tournament. The undefended knight on h5 means Black must be careful: for example 4.e5 Nh5 5.d4 d6 6.Qe2 Be7? (correct is 6...d5! =) 7.exd6 Qxd6 8.Qb5+ wins the h5-knight.[32]

The Modern Defense, or Abbazia Defense,[33] (3.Nf3 d5) has much the same idea as the Falkbeer Countergambit, and can in fact be reached by transposition, e.g. 2.f4 d5 3.exd5 exf4. Black concentrates on gaining piece play and fighting for the initiative rather than keeping the extra pawn. It has been recommended by several publications as an easy way to equalize, although White keeps a slight advantage due to their extra central pawn and piece activity. If White captures (4.exd5) then Black may play 4...Nf6 or recapture with 4...Qxd5, at which point it becomes the Scandinavian Variation of KGA. This variation was considered most critical in the past, but recent trends seem to indicate a slight advantage for White.

"The refutation of any gambit begins with accepting it. In my opinion the King's Gambit is busted. It loses by force." — R. Fischer, "A Bust to the King's Gambit"

The Fischer Defense (3.Nf3 d6), although previously known, was advocated by Bobby Fischer after he was defeated by Boris Spassky in a Kieseritzky Gambit at the 1960 Mar del Plata tournament. Fischer then decided to refute the King's Gambit, and the next year the American Chess Quarterly published Fischer's analysis of 3...d6, which he called "a high-class waiting move".[5][6]

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Fischer Defense after 6.Ng1

The point is that after 4.d4 g5 5.h4 g4 White cannot continue with 6.Ne5 as in the Kieseritzky Gambit, 6.Ng5 is unsound because of 6...f6! trapping the knight, and 6.Nfd2 blocks the bishop on c1. This leaves the move 6.Ng1 as the only option, when after six moves neither side has developed a piece. The resulting slightly odd position (diagram) offers White good attacking chances. A typical continuation is 6.Ng1 Bh6 7.Ne2 Qf6 8.Nbc3 c6 9.g3 f3 10.Nf4 Qe7 with an unclear position. (Korchnoi/Zak)

The main alternative to 4.d4 is 4.Bc4. Play usually continues 4...h6 5.d4 g5 6.0-0 Bg7, transposing into the Hanstein Gambit, which can also be reached via 3...g5 or 3...h6. Today the Fischer's Defense is no longer considered a critical attempt to refute the King's Gambit, and his dream of killing the most romantic opening in chess history remains unfinished.

Joe Gallagher writes that 3.Nf3 Nc6 "has never really caught on, probably because it does nothing to address Black's immediate problems." Like Fischer's Defense, it is a waiting move.[34] An obvious drawback is that the Nc6 may prove a target for the d-pawn later in the opening.

An invention of the Hungarian/English player, János Wagenbach. John Shaw writes: "If given the time, Black intends to seal up the kingside with ...h4 followed by ...g5, securing the extra pawn on f4 without allowing an undermining h2–h4. The drawback is of course the amount of time required".[35]

Of the alternatives to 3.Nf3, the most important is the Bishop's Gambit, 3.Bc4.

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Bishop's Gambit: 3.Bc4

White allows 3...Qh4+ 4.Kf1, losing the right to castle, but this loses time for Black after the inevitable Nf3 and White will develop rapidly. White also has the option of delaying the development of their knight on f3, however, and can instead play g3!?, after which the game becomes quite sharp, with White having the option of Qf3 with an attack on f7, or Kg2 threatening hxg3. This idea is advocated, among others, by GM Simon Williams.[36]

Korchnoi and Zak recommend as best for Black 3...Nf6 4.Nc3 c6, or the alternative move order 3...c6 4.Nc3 Nf6. After 5.Bb3 d5 6.exd5 cxd5 7.d4 Bd6 8.Nge2 0-0 9.0-0 g5 10.Nxd5 Nc6, Black was somewhat better in Spielmann–Bogoljubow, Märisch Ostrau 1923.

Black's other main option is 3...d5, returning the pawn immediately. Play might continue 3...d5 4.Bxd5 Nf6 5.Nc3 Bb4 6.Nf3 Bxc3 7.dxc3 c6 8.Bc4 Qxd1+ 9.Kxd1 0-0 10.Bxf4 Nxe4 with an equal position (Bilguer Handbuch, Korchnoi/Zak).

3...Nc6!? is relatively untested, but if White plays 4.Nf3 Black can transpose into the Hanstein Gambit after 4...g5 5.d4 Bg7 6.c3 d6 7.0-0 h6 (Neil McDonald, 1998).

Steinitz's 3...Ne7 and the countergambit 3...f5 (best met by 4.Qe2!) are generally considered inferior.

Other 3rd moves for White are rarely played. Some of these are:

• 3.Nc3 (Mason Gambit or Keres Gambit)
• 3.d4 (Villemson Gambit[37] or Steinitz Gambit)
• 3.Be2 (Lesser Bishop's Gambit or Tartakower Gambit)
• 3.Qf3 (Breyer Gambit or Hungarian Gambit)
• 3.h4 (Stamma Gambit)
• 3.Nh3 (Eisenberg Gambit)
• 3.Kf2?! (The Tumbleweed[38])

The Falkbeer Countergambit is named after the 19th-century Austrian master Ernst Falkbeer. It runs 1.e4 e5 2.f4 d5 3.exd5 e4, in which Black sacrifices a pawn in return for quick and easy development. It was once considered good for Black and scored well, but White obtains some advantage with the response 4.d3!, and the line fell out of favour after the 1930s.

A more modern interpretation of the Falkbeer is 2...d5 3.exd5 c6!?, as advocated by Aron Nimzowitsch. Black is not concerned about pawns and aims for early piece activity. White has a better pawn structure and prospects of a better endgame. The main line continues 4.Nc3 exf4 5.Nf3 Bd6 6.d4 Ne7 7.dxc6 Nbxc6, giving positions analogous to the Modern Variation of the gambit accepted.

A common way to decline the gambit is with 2...Bc5, the "classical" KGD. The bishop prevents White from castling and is such a nuisance that White often expends two tempi to eliminate it by means of Nc3–a4, to exchange on c5 or b6, after which White may castle without worry. It also contains an opening trap for novices: if White continues with 3.fxe5?? Black continues 3...Qh4+, in which either the rook is lost (4.g3 Qxe4+, forking the rook and king) or White is checkmated (4.Ke2 Qxe4#). This line often comes about by transposition from lines of the Vienna Game or Bishop's Opening, when White plays f2–f4 before Nf3.

One rarely seen line is the Rotlewi Countergambit: 3. Nf3 d6 4. b4!?. The idea of the gambit is similar to that seen in the Evans Gambit of the Italian Game. White sacrifices a pawn to try and build a strong centre with 4...Bxb4 5. c3 Bc5 (or 5...Ba5) 6. fxe5 dxe5 7. d4. However, this line is considered slightly dubious.

Other options in the KGD are possible, though unusual, such as the Adelaide Countergambit 2...Nc6 3.Nf3 f5, advocated by Tony Miles; 2...d6, when after 3.Nf3, best is 3...exf4 transposing to the Fischer Defense (though 2...d6 invites White to play 3.d4 instead); and 2...Nf6 3.fxe5 Nxe4 4.Nf3 Ng5! 5.d4 Nxf3+ 6.Qxf3 Qh4+ 7.Qf2 Qxf2+ 8.Kxf2 with a small endgame advantage, as played in the 1968 game between Bobby Fischer and Bob Wade in Vinkovci.[39] The greedy 2...Qf6 (known as the Nordwalde Variation), intending 3...Qxf4, is considered dubious. Also dubious are the Keene Defense: 2...Qh4+ 3.g3 Qe7 and the Mafia Defense: 1.e4 e5 2.f4 c5.[40]

2...f5?! is among the oldest countergambits in KGD, known from a game published in 1625 by Gioachino Greco.[41] Vincenz Hruby also played it against Mikhail Chigorin in 1882.[42] It is nonetheless considered dubious because 3.exf5 with the threat of Qh5+ gives White a good game. The variation is sometimes named the Pantelidakis Countergambit because GM Larry Evans answered a question from Peter Pantelidakis of Chicago about it in one of his columns in Chess Life and Review.