Relfsson Gambit

The Relfsson Gambit, 1. e4 e5 2. Nf3 Nc6 3. d4 exd4 4. Bb5, replaces the usual recapture on d4 with a Ruy Lopez-style bishop move. White temporarily stays a pawn down, hoping that a later Bxc6 will remove the knight guarding d4 so the pawn can be regained. The engine slightly favors Black, and the line is treated as a curiosity rather than a serious try, although results in online play are close to even.

The most common reply is 4...Bc5, which protects d4 with a piece and has scored well for Black. Against it, 5. O-O is the usual choice, because the attempt to win the pawn back at once, 5. Nbd2 a6 6. Bxc6 dxc6 7. Nb3 Ba7 8. Nbxd4, allows 8...c5 9. Ne2 Qxd1+ 10. Kxd1, and White's king loses the right to castle. The second option, 4...a6, puts the question to the bishop. After 5. Ba4 Nf6 the game transposes into the Mackenzie Variation of the Ruy Lopez, while 5...Bc5 is a frequent alternative. The third most common reply is 4...Nf6.