The Mortimer Trap is a chess opening trap in the Ruy Lopez named after James Mortimer. The Mortimer Trap is a true trap in the sense that Black deliberately plays an inferior move hoping to trick White into making a mistake.
1. e4 e5 2. Nf3 Nc6 3. Bb5 Nf6
5. Nxe5? c6! (see diagram)
6... d6! 7. Ba4 b5
Mortimer played his defense at the 1883 London tournament against Berthold Englisch, Samuel Rosenthal, and Josef Noa, losing all three games. Johannes Zukertort, the tournament winner, also played it against Englisch, the game resulting in a draw. Zukertort wrote of 4...Ne7, "Mr. Mortimer claims to be the inventor of this move. I adopted it on account of its novelty." The first edition of the treatise Chess Openings, Ancient and Modern analyzed 5.Nc3 Ng6 6.0-0 c6 7.Ba4 d6 8.Bb3 and now the authors gave either 8...Be6 or 8...Be7 as giving Black an equal game. A bit more recently, Horowitz and Reinfeld observed of 4...Ne7, "This time-wasting retreat of the Knight to an inferior square blocks the development of the King Bishop ... . Yet it is a matter of record that this pitfall had a vogue for many years."
Today, 4...Ne7 is rarely seen, and is not mentioned in either Modern Chess Openings (which relegates 4.d3 to a footnote, and mentions only 4...d6 in response) or the Encyclopedia of Chess Openings (which mentions only 4...d6 and 4...Bc5).