Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bc4/3...Nf6/4. d4/4...exd4/5. O-O/5...Nxe4/6. Nc3/6...dxc3/7. Bxf7/7...Kxf7/8. Qd5/8...Kf6/9. Qxe4/9...Be7

= Nakhmanson Gambit, Kf6 Defence, Queen Capture =

9...Be7
Black has vacated f8 for the king, and Plan A is to make an immediate dash for f8. For example, if White pretends the last move didn't happen and presses ahead with 10. Bg5+, Black has the simple 10...Kf7 11.Qd5+ Kf8 12.Rae1 Bf6! and all White's invasion routes are blocked.

White can take counter-measures against ...Kf7, though. After 10. Qf4+, the Black king must temporarily rest on g6 (pending ...Bf6 and then ...Kf7), and now one advantage of 9...Be7 becomes apparent: White doesn't have the crushing knight check on h4.

Another attempt to cut the king off from f7 is 10. Ng5, when Black has time to go 10...d5 11.Qf4 Bf5 12.g4 Qd7! and suddenly Black is better developed than White.

10. Re1 carries a subtler threat which, if Black reacts with the automatic 10...Kf7, allows White to escape with perpetual check:  11.Qd5+ Kf8 12.Ng5 and now Black must pin her own bishop with 12...Qe8 to  guard against the mate on f7, because the queen is trapped after 12...Bxg5?? 13.Bxg5. With the bishop paralysed, the White queen can check endlessly on d5 and f5.

The move that shows up 10.Re1 as a serious mistake is 10...d5! denying the queen both the d5 and f5 squares, although Black must not fall for either 11.Qf4+ Bf5?? 12.Qg5+ or 11.Qf4+ Kg6 12.Rxe7 Nxe7?? 13.Ne5+ Kh5 14.Qg5# (the king is safe on h5 after the correct 12...Qxe7 13.Nh4+ Kh5 14.h3 Qe1+ 15.Kh2 Qe5).

Finally there is 10. b4, which may be White's best move. She is trying to either distract the c6-knight away from the defence of e5 and d4 (10...Nxb4?? 11.Qf4+ Kg6 12.Ne5+ Kh5 13.Qg4#) or kick it away. 10...Kf7 is playable but invites 11.b5 with further complications including a future Ba3, so the critical move is again 10...d5! 11.Qf4+ Kg6 12.b5 Qd6! Here White has no good way to keep the queens on and so might as well take the knight, leaving Black with only one extra pawn and the bishop pair in a queenless middlegame.