Hippopotamus Defense: what should White play?

In the position following the initial development of the knights to c6 and h6, White is best served by playing d4 to establish a classical pawn center and take advantage of Black's passive setup. This move is the most popular choice in the database, appearing in 35.6% of the 22,313 recorded games, and it yields a significant engine evaluation of +1.52. By occupying the center, White prepares to exploit the awkward placement of the knight on h6 while maintaining a high win rate of 66.4%.

The central dominance of d4

The move d4 is the primary recommendation for White, as it secures the d4 and e4 squares and opens lines for both bishops. In the main line d4 d6 Nc3 a6 Bc4 Bg4, White continues development while Black remains cramped. Because Black has delayed central tension in favor of the Hippopotamus Defense structure, White is granted the freedom to dictate the pace of the game.

Alternative development with Nc3 and Bc4

If White prefers a piece-led approach, Nc3 and Bc4 are highly effective alternatives. Nc3 has been played in 16.7% of games and carries an evaluation of +1.30, often leading to sequences such as Nc3 e5 d4 exd4 Nd5 Ng4. Meanwhile, Bc4 is the second most frequent choice at 25.5%, scoring 63.5% for White. This move targets the f7 weakness, which is particularly relevant if Black attempts to strike back with f5 as seen in the line Bc4 f5 e5 e6 d4 Nf7.

Prophylactic and restrictive options

White may also consider h3 or Bb5 to limit Black's counterplay. While h3 is only played in 2.1% of games, it effectively prevents any future pins on the f3 and prepares a solid foundation for the center. Bb5 is more common (7.8%) and aims to disrupt Black's queenside structure, leading to positions like Bb5 a6 Bxc6 bxc6 d4 g6, where Black is left with doubled pawns in exchange for the bishop pair.