Tennison Gambit

The Tennison Gambit arises from 1. e4 d5 2. Nf3, or from the Zukertort move order 1. Nf3 d5 2. e4, and is classified under ECO A06. Instead of capturing on d5 as in the Scandinavian Defense, White leaves the e-pawn hanging. The bet is that the tempo Black spends taking it, and the exposed pawn on e4, will hand White a lead in development and chances against f7. The opening takes its name from Otto Mandrup Tennison (1834–1909), a Danish-born amateur who emigrated to the United States and played in the chess clubs of New Orleans. He was the first to study it seriously, and stronger players adopted it in the first half of the twentieth century.

Accepting with 2...dxe4 is by far the most frequent reply and the critical test. The capture attacks the knight, and 3. Ng5 is the main line, hitting e4 and eyeing f7. White aims either to regain the pawn with better development or to punish Black for clinging to it. The usual remedy is to give the pawn back with 3...e5. Black stands better after 4. Nxe4 f5, and also after 4. h4 Be7 5. Bc4 Bxg5 6. Qh5 g6 7. Qxg5 f6. The bishop sortie 3...Bf5 is also good, and 4. g4 Bg6 5. Bg2 h5 leaves Black ahead in a sharp position. The natural 3...Nf6 gives White more play. In Ermenkov–Bonchev, Bulgaria 1970, White kept an edge after 4. Bc4 e6 5. Nc3 a6 6. Ngxe4 Nxe4 7. Nxe4 b5 8. Be2 Bb7 9. Bf3. The named Brigg's Trap also starts from this knight move, with 3...Nf6 4. Nc3 Bf5 5. Qe2 Qd4.

Black can also decline and steer into familiar defenses. 2...e5 is the Elephant Gambit. 2...e6 heads for the French, for example an Exchange French after 3. exd5 exd5 4. d4. 2...c6 reaches the Caro-Kann, either the Two Knights line after 3. Nc3 or an Exchange structure after 3. exd5 cxd5 4. d4. Declining with 2...Nf6 allows 3. e5 Nfd7 4. d4, and White's central space makes the game easier. The advance 2...d4 is dubious. After 3. c3 c5 4. cxd4 cxd4 5. Qa4+ Nc6 6. b4, the coming b5 drives away the knight that guards d4, and the pawn falls.

Theory regards the gambit as unsound, since White gets no lasting positional return for the pawn, and the engine gives Black a clear advantage after 2. Nf3. In practice it is a different matter. The position is among the more frequently reached named openings in online play, and results there are close to level, because Black must meet the threats against e4 and f7 accurately. Tennison's own game against an unnamed opponent in New Orleans in 1891 shows the attacking idea: 2...dxe4 3. Ng5 f5 4. Bc4 Nh6 5. Nxh7 led to a quick king hunt.