Rapport had already played like that in the past. He is trying to make use of the fact that c7-c5 is not possible at the moment.
1. g1f3 Rapport needs only a win and, therefore, decides to avoid the classical theoretical lines on which his opponent has built his opening repertoire. 1... d7d5  2. g2g3  2... g8f6  3. f1g2  3... e7e6  4. e1g1  4... f8e7  5. d2d3  5... e8g8  6. b1d2 There is revived interest in the King's Indian Attack. 6... b8c6 Which, in turn, forces Black to search for new resources. The move in the game prepares e6-e5, effectively entering into a reversed Pirc.