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...Ke8/9. Re1/9...Be7/10. Rxe4/10...d6

= Nakhmanson Gambit, Ke8 Defence =

10...d6
11.Bg5 is the only move to disrupt Black's plan of ...Rf8 and ...Bf5. The tempting 11.Ng5? only encourages it: 11...Rf8 12.Nxh7 Bf5!

11...Rf8 amounts to the same thing as on the previous move - Black must eventually trade Q+N for R+R on e7.

After 11.Bg5, Black has to step out of the pin with 11...Kf8 to be able to move the bishop from e7. Then White might as well gain a tempo on the bishop anyway with 12.Rae1, forcing 12...Bf6 (definitely not 12...Bxg5 which allows  mate in 7). Then White keeps up the pressure with 13.b4, to which Black responds 13...Qd7, placing the queen on a defended square and so preparing to  respond to b5 with ...Ne5.

Now both players transfer their attentions to the bishop on f6 - White to trying to capture it, Black to defending it. 14.Rf4 Ne7 15.Qb3 (or 15.Qd3) 15...Ng8 16.Qxc3 Qd8 (16...Qf7 invites a future Ng5) 17.Re3!

Black still has the extra piece, but is in a serious bind. She has to keep three defenders on f6 - queen, knight and g7 pawn. The d-pawn must stay on d6 to keep the knight out of e5, and the h-pawn must stay on h7 to keep it out  of g6 (via h4). The light-squared bishop is needed to guard e6 against the Nf3-d4-e6 royal fork, and putting it on d7 allows White to take on g5 and  play Ng5, with Qc4 to follow threatening mate on f7. Pushing the c-pawn allows White to pile up on f6 some more with Nd2, Ref3 and Ne4, since ...d5  would invite Qc5+ and Black no longer has ...Qd6 to block.

This is a lot to keep track of, but the upshot is that any seemingly constructive Black move will be worse than saying "pass", which is a position Black wouldn't have found herself in if she'd played 8...Kf6.