1.Nf3 f6 2.e3 d5 3.Ne5 Bg4

White can play 4.Qf3 and black has a difficult game:

4...e6 5.Nf7 Qc8 (or 5...Qe7) 6.Bb5 c6 7.Nd6+ (or 7.Qg3 e5) Bxd6 8.Qf4 e5 9.Ba6,

4...g5 loses to 5.Nd7 Bh6 6.Bd3 Bxf3 7.Bxh7 Nc6 8.Nc3,

4...g6 5.Nf7 Qc8 6.Bb5 c6 7.Ba6 bxa6 8.Qf4 Qf5 (8...Na6 9.Qb8 Nb4 (9...e5 10.Qb7 Nc7 11.Nd6+ Ke7 12.Qb4 c5 13.Qa5 and black is lost) 10.Qb7 Qxb7 and white is winning) 9.Qxg4 and white is a pawn up.

Another possible line: 4.f3 fxg5.