A rare move that caught the players with Black by surprise. 7.Bg5 and 7.Bxd6 are more common.
1. d2d4  1... d7d5  2. c2c4  2... e7e6  3. b1c3  3... a7a6  4. c4d5  4... e6d5  5. c1f4  5... g8f6  6. e2e3  6... f8d6 