Ruy Lopez: Noah's Ark Trap
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 b5 5.Bb3 d6 6.d4 Nxd4 7.Nxd4 exd4 8.Qxd4 c5
Noah's Ark Trap
1.2.3.4.5.6.7.8.
What Is The Noah's Ark Trap?
White's 6.d4 strikes the centre before the light squared bishop has an escape square. Black answers 6...Nxd4 7.Nxd4 exd4 8.Qxd4 c5, hitting the queen, and after 9.Qd5 Be6 10.Qc6+ Bd7 11.Qd5 c4 the bishop on b3 is caught. a2 and c2 are blocked by White's own pawns and a4 is covered by the b5 pawn, so Black wins a piece.
The cure is 6.c3 first, which gives the bishop c2 and makes d4 safe; that is why the main Ruy Lopez is built around c3. Do not file this as a one move trick. The same box recurs in many lines: with a bishop on b3 and Black pawns on a6 and b5, ...c4 is a resource you must calculate every time you open the centre.