The idea of this move is to prevent the bishop from going to b5.
1. d2d4  1... d7d5  2. c2c4  2... c7c5 [%c_effect c5;square;c5;type;Interesting;persistent;true][%cal dc7c5][%c_arrow c7c5;keyPressed;none;from;c7;opacity;0.8;to;c5;persistent;false] Nakamura has played this provocative move other times. 3. c4d5  3... g8f6 A rare move that is new to Nakamura's practice. Previously he had captured on d5 immediately with the queen. The game, however, will soon transpose to a more conventional position. 4. b1c3 Ding decides not to get into a discussion about the validity of Black's defense; otherwise, he would have to play one of the alternatives. 4... f6d5  5. g1f3 This is a well-known position of opening theory. 5... c5d4 Another move that is not played often. 6. d1d4  6... d5c3  7. d4c3  7... b8c6  8. e2e4 