Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Ba4/4...Nf6/5. O-O/5...Be7/6. Re1/6...b5/7. Bb3/7...O-O/8. c3/8...d5

Ruy Lopez, Marshall Gambit
Black is attacking e4 twice and in general threatening to overrun the centre of the board. White has no better option than to accept the proffered pawn with followed by capturing twice on e5. Skip ahead to the end of that forcing variation if you like: 9. exd5 Nxd5 10. Nxe5 Nxe5 11. Rxe5.
 * 9. exd5

However, White can also decline the gambit with 9.d4.