The Schliemann Defense (3 ... f5) is a popular try for Black in the amateur ranks. This gambit leads to wild positions in which White must know certain theoretical lines in order to escape with an advantage. Conversely, an unprepared White player will struggle to navigate the challenges posed by Black. White's best response is 4. Nc3, but Black certainly has many ways to create an interesting and tactical game. At higher levels, where White is more likely to be prepared, the Schliemann Defense is used only rarely as a surprise weapon.
This opening is also known as the Jaenisch Gambit.