Lesson
White to move. Main line: 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 d6 5. d4 b5 6. Bb3 Nxd4 7. Nxd4 exd4 8. Qxd4 c5 9. Qd5 Be6 10. Qc6+ Bd7 11. Qd5 c4
The premature 5.d4 lets Black strike with ...b5 and ...Nxd4, and after the queen recaptures on d4 the pawns march: ...c5 gains a tempo on the queen, and ...c4 finally shuts the door on the b3-bishop, which is snared behind the a6/b5/c4 pawn chain.
The name comes from the pawns closing over the bishop “two by two.” The lasting lesson: in the Ruy Lopez the d4-break needs preparation — played too early it hands Black the ...b5/...c5/...c4 pawn storm for free.