Poli Gambit

English Defense

1.d4 b6 2.c4 e6 3.e4 Bb7 4.f3 f5 5.exf5 Nh6

White props up e4 with f3, and Black gives a pawn with ...f5 to bring the knight to f5.

The idea

After 4.f3 f5 5.exf5 Nh6, Black has given up a pawn to open lines. The knight heads for f5, taking back the pawn and hitting d4 and e3, while f3 has weakened White's kingside, including the e1-h4 diagonal.

Plans for White

Develop quickly and keep the king safe. Nc3, Bd3 and Nge2 are natural. White can try to keep the extra pawn with g4, but that weakens the kingside further, so returning the pawn for a safe position is also reasonable.

Plans for Black

Take back on f5 with the knight, then develop with ...Bb4+, ...O-O and ...Qh4+ ideas against the weakened dark squares. Black wants to make use of f3 having taken away the knight's best square.

Watch out for

For White, ...Qh4+. With the f-pawn on f3, the diagonal from h4 to e1 is open, and the check can come with gain of time or with an attack on e4 or g3.

For Black, getting nothing for the pawn. If White develops and castles safely, Black is just a pawn down.