Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Ba4/4...Nf6/5. O-O/5...Nxe4/6. d4/6...exd4/7. Re1/7...d5/8. Bg5/8...Be7

=Ruy Lopez, Riga Variation=

Black interposes his bishop between his queen and white's g5 bishop. Usually this means black is willing to trade bishops, as white almost always takes with 9. Bxe7. White has no better move, as his bishop is threatened, under attack from two pieces and defended only by the f3 knight.

Black can take back with 9...Kxe7 or 9...Qxe7, however 9...Kxe7 is considered correct as it frees black's c6 knight from the pin.

9...Kxe7 is usually followed with 10.Bxc6 bxc6 11.Qxd4 from white, winning back a pawn.

9...Qxe7 means that white still has two pins going, and he will try to make the most of that with moves like 10.c4 which threaten to unhinge black's pinned knight in the center.