Anti-Philidor

The Anti-Philidor is White's most ambitious answer to the Lion Defense. With 4. f4, White puts pawns on d4, e4 and f4 and adds a second attacker to e5, the square Black's whole setup is built around. It is generally regarded as the sternest test of the system. The engine gives White a slight edge, and White's practical results are somewhat better than in the more common 4. Nf3.

Black nearly always insists on 4...e5, the Lion's Cave, which accounts for roughly four games in five. The f-pawn changes the follow-up. After 5. Nf3, Black cannot simply hold the center. The natural 5...Be7 fails to 6. fxe5 dxe5 7. dxe5, winning a pawn, so Black has to release the tension with 5...exd4 and fight for counterplay against White's extended center. The fianchetto with 4...g6, which turns the game back toward Pirc lines, and the flexible 4...c6 are the main alternatives. Both are much less common, and White scores well against 4...g6.