Nimzowitsch Attack
Petrov's Defense
1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 4.Nf3 Nxe4 5.Nc3 Nxc3 6.dxc3
White trades off Black's knight with 5.Nc3, accepting doubled pawns for fast development.
Fun fact: Viswanathan Anand resigned after only six moves against Alonso Zapata at Biel in 1988, after falling for the 5...Bf5?? 6.Qe2 pin. Source
Practice this lineThe idea
Instead of supporting d4, White trades the knight on e4 with 5.Nc3 Nxc3 6.dxc3. White's c-pawns are doubled, but the d-file is open, the queen's bishop is free, and White can castle queenside quickly.
The game is often sharper than the main line, with the kings on opposite sides.
Plans for White
Develop with Be3, Qd2 and O-O-O, then attack Black's king with the kingside pawns. The open d-file and quick development make up for the doubled pawns.
Plans for Black
Develop with ...Be7, ...O-O and ...Nc6 or ...Nd7. Black is solid and has the healthier pawns, so a quiet game or an endgame is fine for Black. If White castles queenside, Black can counterattack there with ...c5 and ...b5.
Watch out for
For Black, developing the bishop too early. After 5.Nc3, the natural-looking 5...Bf5?? loses a piece to 6.Qe2: the knight on e4 is pinned to the king, and after 6...Qe7 7.Nd5 Qd7 8.d3 it falls.
For White, an attack without preparation. Black's position has no weaknesses, so White needs to castle and bring pieces over before pushing pawns.
The pin on the e-file (5...Bf5??)
5...Bf5 6.Qe2 Qe7 7.Nd5 Qd7 8.d3