Been-Koomen Variation

The Been-Koomen Variation departs from the Orthodox treatment of 4. Bg5. Instead of breaking the pin with 4...Be7 or preparing a slow ...c5 after castling, Black plays the freeing break immediately. The move ignores the pressure on the f6-knight and challenges d4 before White has finished developing. The cost is that Black's kingside is still undeveloped. The pin on f6 then becomes more awkward, because exchanges in the center can open lines while the black king remains in the middle.

White has three main replies. 5. e3 is the most popular and keeps the central tension, supporting d4 and preparing to develop the kingside. 5. cxd5 releases the tension and leads to the Pseudo-Tarrasch Variation, where structures with an isolated or hanging pawn are typical. 5. Nf3 transposes to the Pillsbury Variation of the Semi-Tarrasch Defense. The engine also considers 5. Bxf6, which gives up the bishop to damage Black's structure or deflect a defender of d5. The position is rated as roughly balanced with a small plus for White. The variation is not common, but Black's practical results are respectable, and it is less theoretical than the main Orthodox lines.