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. Re1/9...Ne7/10. Qxe4/10...Kf7/11. Bg5

= Nakhmanson Gambit, Kf6 Defence, Rook Attack =

11. Bg5
The immediate 11...Kg8 is too compliant. With the e7-knight pinned, White doesn't have to take three times on e7 straight away, but can resolve the pawn  situation with 12.bxc3 and restore material equality.

Black can't remove the pin just yet. 11…Qe8 is just stepping out of one pin into another, and does nothing to free the knight. But with 11...d5, Black can at least prepare to remove the pin.

Or Black can resolve the pawn situation herself with 11...cxb2, now that the bishop can't recapture from c1.

It turns out that with best play 11...d5 and 11...cxb2 transpose into each other, but 11...d5 is a better practical choice because the juicy morsel on c3 might tempt White into accidentally losing a piece.