Originally posted by 7ate9
Can someone please explain Topalov's castling. e.g. How he can leave black's a3 pawn alone?
Also was the h2 pawn given to trade for a central secured setup with his knight?
I think the h2 pawn was for speed of development. The a3 pawn could be left since black would need far too many moves to adequately defend it than were possible.
So after the opening he was one pawn down 'in spirit' since the a3 pawn was lost in the short term. But in the long run, both of Kramnik's remaning queenside pawns were weak on a7 and c6. Two open files, and Topalov's pieces primed to attack them. An extra pawn yes, but when two pawns are likely to drop, this is not so good. So Kramnik sac'd one to get some play, levelling up the material.
So: A completely stranded pawn can usually be mopped up later when conditions are right, there is no need to rush to recapture in such a case. And sacrificing one of your pawns to weaken two of your opponents can be a very good plan. We saw both these themes today in the opening/early middle-game; hope this helps.