Normal Variation, Rare Defenses

The move 5. Nf3 develops the king's knight behind White's broad center of pawns on c4, d4 and e4. Every one of those pawns is protected and White has no weaknesses, while the choice of where to put the king's bishop is still open. Although the line is catalogued as Rare Defenses, the name is a label for this junction rather than a description of the play. Black's usual reply is entirely conventional, and the rarer tries are minor alternatives to it.

Black castles with 5...O-O in close to four games out of five, and this is also the engine's first choice. Castling is a useful preparatory move rather than a waste of time. The immediate central strike 5...e5? fails to 6. dxe5 dxe5 7. Qxd8+ Kxd8 8. Nxe5 Nxe4 9. Nxe4 Bxe5 10. Bg5+ Ke8, which leaves White better with Black's king stranded in the center. Once the king is on g8, Black can challenge the center with ...e5 or ...c5. The most common route is 6. Be2 e5 7. O-O, the main line of the Classical system.

The two other moves seen with any frequency both postpone castling. 5...Bg4 pins the f3-knight and puts pressure on White's control of d4, which is the square the knight is meant to cover. White scores slightly better against it than against 5...O-O. 5...Nbd7 is a quieter, flexible move that places the knight behind the e-pawn in support of a later ...e5. The engine also lists 5...Na6 among its top choices, another way of developing the queen's knight without blocking the c-pawn.

The engine gives White a slight edge, which is typical of the King's Indian main lines. In online play the results are almost evenly split, with White marginally ahead, and draws account for under five percent of games. The ...O-O lines lead into the familiar strategic pattern of the opening. If White closes the center with d5, Black generally turns to ...f5 and a kingside attack or to ...b5 and queenside play, and White expands on the opposite wing. Both sides keep realistic winning chances in these unbalanced positions.