Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...f5/4. d3/4...fxe4/5. dxe4/5...Nf6

Ruy Lopez, Schliemann Defence

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

Common moves:
6. O-O - Main Line

There are a few minor moves here, but if White notices that she doesn't have to directly defend the e-pawn, then 6. O-O makes the most sense, avoiding a potential pin or check after 6... Bb4, which would allow Black to develop the dark squared bishop and play d6 more easily. 6... Nxe4? in response would be a tactical error, allowing 7. Re1 or Qe2 with a strong attack along the e file, as 7... d5 allows 8. Nxe5 with the c6 knight pinned.

Wikipedia has related information at Ruy Lopez