Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. c3/3...f5

3...F5
This is the dangerous but exciting Ponziani Countergambit. It sacrifices the F pawn, but attacks E4 and prepares the develop the G1 knight. While 4.Exf5 is a good move, 4.D3 and 4.D4 are better options. If white has studied against this, black will have a bad time, but if not, both black and white will be able to attack in an exciting game.