Four Pawns Attack

Alekhine's Defense

1.e4 Nf6 2.e5 Nd5 3.d4 d6 4.c4 Nb6 5.f4 dxe5 6.fxe5 Nc6 7.Be3

White builds a huge center with f4, and Black hits it at once.

The idea

After 5.f4 dxe5 6.fxe5 Nc6 7.Be3, White has a huge center, and Black's knight on c6 attacks d4. Wikipedia gives this as the main line, and warns that passive play by Black will be crushed by the white center.

Plans for White

Develop with Nc3 and Nf3, protect e5 and d4, and push d5 when it gains space or time. Wikipedia notes 7.Nf3 allows 7...Bg4!, when the pressure on d4 is very hard to meet, which is one reason for 7.Be3.

Plans for Black

Develop with ...Bf5, ...e6 and ...Qd7 or ...Be7, castle (sometimes queenside), and keep hitting d4 and e5. Black's pieces must create threats quickly, before White's center rolls forward.

Watch out for

For Black, being passive. Once White's center is supported, it can push d5 and e6, and Black's pieces get pushed back.

For White, the dark squares and d4. With pawns on c4, d4 and e5, the squares behind them can become weak, and ...Bg4 or ...Nc6 can pile up on d4.