The Marshall defence goes 1. d4 d5 2. c4 Nf6?!
I played this game recently as white. It was the first time I saw the Marshall in a game and the real contest was over by move 14.
[FEN ""]
[StartPly "7"]
1. d4 d5 2. c4 Nf6 3. cxd5 Nxd5 4. Nf3 Bg4 5. e4 Nb6 6. Be2 Bxf3 7. Bxf3 e6 8. O-O Be7 9. d5 O-O 10. dxe6 fxe6 11. Qb3 Qd7 12. Bg4 Rf6 13. Rd1 Bd6 14. e5 Rg6 15. exd6 Rxg4 16. dxc7 Rd4 17. Rxd4 Qxd4 18. Qxe6+ Kf8 19. c8=R+ Nxc8 20. Qxc8+ Ke7 21. Qxb7+ Kf6 22. Qf3+ Ke6 23. Qe3+ Qe5 24. Nc3 Nc6 25. f4 Qxe3+ 26. Bxe3 a5 27. Rd1 Ne7 28. Nb5 Rb8 29. a4 Nd5 30. g4 Nxe3 31. Re1 Rf8 32. Rxe3+ Kd7 33. f5 g6 34. Rf3 Kc6 35. Kg2 gxf5 36. Rxf5 Rg8 37. Kf3 Rd8 38. Kg3 Rd3+ 39. Rf3 Rd2 40. b3 Rb2 41. Na3 Ra2 42. Nc4 1-0
Now the Marshall defence is considered to be dubious, even refuted:
This [1. d4 d5 2. c4 Nf6?! 3. cxd5 Nxd5 4. Nf3!] is considered to be the refutation for this defence
Source: GreenCastleBlock on YouTube, @ 0:58.
But my question is there any move after 4. Nf3 where black gains equality?
22. Bd2
looks more convincing.