Noteboom Variation, Anti-Noteboom Variation, Belyavsky Line

The Belyavsky Line, 5...f6, blocks the bishop's diagonal toward d8 with a pawn and gains a tempo against the bishop, while Black keeps the extra pawn on c4. The cost is a loosened e6-pawn and kingside. White must move the bishop. 6. Bh4 is by far the most common retreat, 6. Bf4 comes next, and 6. Bd2 is rare even though the engine prefers it. White scores well in practice, and the engine gives White a slight edge.