Chess Opening Theory/1. e4/1...e5/2. f4/2...exf4/3. Nf3/3...g5/4. h4/4...g4/5. Ne5/5...d6

Kieseritzky Gambit

	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. Nxg4 - only move

6. Nxg4 is the only sensible move, otherwise it's not clear how White will ever recover the pawn on g4.

Wikipedia has related information at King's Gambit.