A question on Spanish game which I get quite frequently from my students

Avebakh vs Smyslov, Zurich 1953

Q:

White has just played 9. h3 to prevent  9......Bg4.

What if  Black played this move earlier( before castling) - 8......Bg4 instead of 8.....O-O? Then how does White go about to get rid of this troublesome pin? Is it by 9.h3 followed by 10.d3 followed by Nbd2 , Nf1 , Ng3?

A:

All the key idea to undertand it is that the pin  Bg4 in this case is dangerous only in case White makes the move d4 (then the Bg4 does there a concrete job - takes part in the pressure against the d4 pawn and White's centre at the same time). 

Thus it becomes clear too that White makes this move h3 because he wants to continue with d4, which he usually makes there on a following move.

And when the pawn in not moved yet to d4, or just to d3, then Bg4 makes much less sense, and on the contrary Black usually avoids making this pin, because the Bishop itself can become an object of attack there, and will be at a risk either to be exchanged for the Nf3 (which means a loss of Bishop pair for Black and weakening a complex of important light squares around his Kingside), or to retreat via h5 to g6, where it often turns out to be more like a burden when it comes to defense of Kingside rather than a help, and especially when the pawn e4 will be protected by another pawn d3 it may be very limited on that diagonal, unlike in case the pawn is already moved to d4 (then the e4 one can become a target for the Bishop on g6 and the whole diagonal is much more open). And also White can make his pawns rolling on Black's Kingside by means of g4-h4-h5 while driving the Bishop away this way. 

And right, the right plan against this pin is the normal development for this scheme by means of d3,  Nd2-f1-g3, h3 (or in some cases h3 can be made earlier too), and this is the case the Bishop already finds itself in an awkward position;  the square h5 is not that convenient for it  anymore because of the Knight standing on g3. That's it.