Nimzowitsch Variation, Klein Variation

Instead of defending e4 with 4. Nc3, White develops the bishop and lets Black take the pawn, counting on threats against f7. The point shows after 4...Nxe4 5. dxe5: if 5...dxe5, then 6. Qxd8+ Kxd8 7. Nxe5 hits f7 again, and against most other fifth moves White has the sacrifice Bxf2+, answering the king's recapture with Qd5+ to fork the king and the e4-knight. The usual remedy is 5...c6, which takes d5 from the queen and prepares ...d5 to shore up the knight. Engines still rate the capture 4...Nxe4 among Black's best options.

Black can also decline the material. The most frequent reply is 4...Nc6, which leads to the Italian Game: Scotch Invitation Declined. The engine's top choice is 4...exd4, and after 5. Nxd4 Be7 6. Nc3 play usually transposes to the Exchange Variation of the Philidor; in the database this capture gives the most even results. The line is an uncommon alternative to 4. Nc3, and engines regard the position as roughly balanced.