All of Black's play came from the pin on f3. Around about here.


White usually stops for h3 to prevent the Bg4 pin so the f3 Knight can bolster d5.
I've seen games without it and a different plan adopted but this is a drastic
example of allowing Bg4 and going for d4.

The strategic inaccuracy is 10. Bg5. It looks harmless, but in fact commits the B prematurely. 10. Nbd2 is fine; developing the QN before the QB is standard in the RL Also 10. h3 is absolutely fine too.

But White cannot play blindly. B has played the significant ...Re8. White could play 10. Ng5 (hitting f7) and forcing a repetition if Black wants it (...Rf8; Nf3 Re8; Ng5 etc). But White must not neglect defence of his e4 in any of the lines. Hence Nbd2 or even Bc2 come into it. Also d5. 10. Bg5 is too slow though, and misplaces the bishop