Two Knights Defense, Perreux Variation

The Perreux Variation takes the Open Variation of the Two Knights Defense in a direct direction. After 4. d4 exd4, White neither castles (5. O-O) nor kicks the knight (5. e5). Instead 5. Ng5 aims the knight and bishop at f7 at once, despite the missing pawn. The approach is regarded as dubious: Wikibooks calls the attack misguided, and the engine gives Black a slight edge. Even so, White scores well in online games and draws are rare, since the position is full of traps for an unprepared defender.

The most common and most highly regarded answer is 5...d5 6. exd5 Qe7+. Here White usually gives up castling with 7. Kf1 rather than block the check. About a fifth of players choose 5...Ne5, which defends f7 and harasses the bishop. Typical lines are 6. Qxd4 Nxc4 7. Qxc4 d5 8. exd5 Qxd5 9. Qe2+, which simplifies, and the sharper 6. Bb3 h6 7. f4 hxg5 8. fxe5 Nxe4. The check 5...Bb4+ is a rarer alternative.