If White does so, the game quickly takes on a tactical character: Black is practically forced to give up a pawn for the initiative.

The complications are such that David Bronstein suggested that the term "defense" does not fit, and that the name "Chigorin Counterattack" would be more appropriate.

In modern grandmaster play, 3.Bc4 is less common than 3.Bb5, and the more solid 3...Bc5 is the most frequent reply, so the Two Knights Defense is infrequently seen.

The theory of this opening has been explored extensively in correspondence chess by players such as Hans Berliner and Yakov Estrin.

German master Siegbert Tarrasch called 4.Ng5 "a real duffer's move" (ein richtiger Stümperzug) and Soviet opening theorist Vasily Panov called it "primitive", but this attack on f7 practically wins a pawn by force.

Then Black usually plays 5...Na5 but there are other options: After 5...Na5, the Polerio Defense,[7][8] Paul Morphy would play to hold the gambit pawn with 6.d3, the Kieseritzky Attack (or Morphy Variation), which has not been popular, since it has long been known that Black obtains good chances for the pawn with 6...h6 7.Nf3 e4 8.Qe2 Nxc4 9.dxc4 Bc5.

(The move 8.Qf3, popular in the nineteenth century and revived by Efim Bogoljubow in the twentieth, can be played instead; Black may reply with 8...h6, 8...Rb8, or 8...Be7.)

The wild Nakhmanson Gambit 6.Nc3 gives White compensation if Black accepts the piece with 6...dxc3 7.Bxf7+ Kxf7 8.Qd5+ and then makes the intuitive move 8...Ke8?!

[16] Alternatively, Black can enter the extensively analyzed Max Lange Attack after 5...Bc5 6.e5 d5, which can also arise by transposition from the Giuoco Piano or Scotch Game.

The quiet move 4.d3, the Modern Bishop's Opening,[17] transposes into the Giuoco Pianissimo if Black responds 4...Bc5, but there are also independent variations after 4...Be7 or 4...h6.

White tries to avoid the tactical battles that are common in other lines of the Two Knights and to enter a more positional game.

The resulting positions take on some characteristics of the Ruy Lopez if White plays c3 and retreats the bishop to c2 via Bc4–b3–c2.

This gambit is not commonly seen in tournament play as it is not well regarded by opening theory, but it can offer White good practical chances, especially in blitz chess.