Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. c3/3...Nf6

= Ponziani Opening, Jaenisch Counterattack =

3. Nf6
The point of this defense is to create an attack on e4 and white cannot defend this pawn with Nc3 because c3 pawn and Nd2 because d2 pawn.