Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bc4/3...Nf6/4. Ng5/4...Bc5/5. Nxf7/5...Bxf2

5...Bxf2+
The main idea of the Traxler Counterattack. Ignoring White's fork, Black aims to gain tons of space on the board and move all their pieces out to attack the wide open king. Impressively, Black will be able to gain their lost material if played correctly.

White can capture with Kxf2, but Black more easily be able to launch a counterattack, starting with Nxe4+. Thus experienced players generally prefer Kf1.