Quite a risky move, unless it was prepared beforehand; as I wrote before, this is not clear to me.
1. e2e4  1... e7e5  2. g1f3  2... b8c6  3. f1b5  3... a7a6  4. b5a4  4... g8f6  5. e1g1  5... f8e7  6. d2d3  6... b7b5  7. a4b3  7... d7d6 Together with 8.a4 and 8.c3, this is one the main lines of this Ruy Lopez system. 8. a2a3  8... c6a5 A known move, but much rarer than the most natural castling. 9. b3a2  9... c7c5  10. b1c3  10... c8e6  11. c1g5 A solid and typical move. The plan is to capture the knight and gain control of the d5-square. 11... e8g8  12. g5f6  12... e7f6  13. c3d5  13... g7g6  14. d1d2  14... f6g7 A new move, but as usual in this match, it's never clear to me if Ding has the position prepared or if he's improvising on the board. 15. f3g5 [%c_effect g5;square;g5;type;GreatFind;persistent;true] This is the problem. Now this unpleasant knight move is possible.