Vienna Hybrid, Hromádka Variation

The Hromádka Variation is White's response to the pin 4...Bb4 in the Vienna Hybrid. With the c3-knight pinned, the king's knight goes to e2 rather than f3. The square serves two purposes. If Black captures on c3, White can recapture with the knight instead of a pawn, keeping the queenside structure intact. The f-pawn also stays unblocked, so f4 remains available as a way to give the game a King's Gambit flavor once development is complete. The cost is a somewhat passive knight and a later start to kingside castling than after Nf3.

Black's three main replies are about equally popular. 5...O-O simply completes development. 5...d6 is a solid way to support e5. 5...d5 strikes at the center before White can organize f4, and Black scores best with it in online games. The engine ranks 5...d5 first, followed by 5...Bc5 and 5...d6, and considers the position level. In Lichess games White still wins more often than Black, and draws are rare.