The Marshall Defence is a chess opening that begins with the moves: 1. d4 d5 2. c4 Nf6?!
It is a dubious variation of the Queen's Gambit Declined. It was played by Frank Marshall in the 1920s, but he gave it up after losing with it to Alekhine at Baden-Baden in 1925. It is no longer used by experienced players.
White may choose to ignore Black's provocative second move with 3.Nc3, which will usually transpose into normal lines of the Queen's Gambit Declined (after 3...e6), the Slav Defence (after 3...c6), the Queen's Gambit Accepted (after 3...dxc4) or the Grünfeld Defence (after 3...g6).