A known move, but much rarer than the most natural castling.
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 