Black makes a temporary sacrifice of the knight, and if White plays 5.Nxe4, Black can play ...d5 with a fork which wins back the piece. This tactical trick does not win any material for Black, but knocking out the important White center pawn on e4 has secured Black a good foothold in the center.

Even so, 5.Nxe4, falling in with Black's plan is White's best move. 5.Bxf7+ looks good at first glance because Black's king gets slightly exposed, but White is not developed enough to sustain an attack. 5.O-O can cause problems for black if they are not careful.

The tactic employed by Black is called the "Fork Trick" and pops up in a number of openings, but it is particularly potent in the Four Knights.

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1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4.Bc4 Nxe4!

Wikipedia has related information at Four Knights Game.

• Evans, Larry D. The Fork Trick. Published in two parts (April 2000 and May 2000) issues of Chess Life. Online facsimiles of the articles are available at chesscamp.net.