Modern Variation, Knight Defense

The Knight Defense answers the pin with 4...Nbd7 and leaves the f8-bishop undeveloped for now. The knight supports f6 and keeps open the plan of ...c6 and ...Qa5. After 5. e3 c6 6. Nf3 Qa5, or the same position reached by 5. Nf3 c6 6. e3 Qa5, the game becomes the Cambridge Springs Defense. There the queen unpins the knight and pins the c3-knight along the a5–e1 diagonal. The move also sets the Elephant Trap. After 5. cxd5 exd5 the obvious 6. Nxd5?? fails to 6...Nxd5, because 7. Bxd8 is met by 7...Bb4+ 8. Qd2, and Black regains the queen and comes out a minor piece ahead.

The most common reply is 5. e3, followed by 5. Nf3. Played correctly, 5. cxd5 exd5 leads to an Exchange Variation structure, and White uses it to sidestep the Cambridge Springs. The engine favors this capture, yet Black scores better than White after it in online games. The engine assesses the position as roughly balanced, and decisive results greatly outnumber draws.