\"Fabiano [Caruana] made this move popular. He played it in Paris two years ago.\" (So). Black keeps his kingside knight undeveloped for the time being in order to avoid the pin with Bc1-g5.
1. e2e4  1... e7e5  2. g1f3  2... b8c6  3. f1c4  3... f8c5  4. d2d3  4... d7d6  5. c2c3 