Scheveningen Variation, Keres Attack

Introduced by Paul Keres in 1943, 6. g4 exploits the fact that ...e6 has closed the c8-bishop's path to g4, so White can follow with g5 to dislodge the f6-knight. The most frequent answer, 6...h6, stops the advance but leaves White with extra kingside space and makes castling there less appealing for Black; White may later develop with Bg2. 6...Be7 and 6...a6 are the main alternatives. Theory holds that Black can hold the balance, although the engine gives White a slight edge, and many players reach the Scheveningen via 5...a6 to avoid this line.