Getting castling wrong

The last game of the now postponed 2020 Candidates tournament featured a nice win by Maxime Vachier-Lagrave over Ian Nepomniachtchi. Early on in the game Nepo played his rook to g8, and soon played his king to f8.  If I seen a position in one of my coaching classes I  might have been tempted to stop and explain the rules of castling to both players.
On further inspection it wasn't moving the king to f8 that was the problem. Black was doing OK until he chose another move that is often risky for French players, and that was c4. Removing the pressure on d4 often leads to an advantage for White and so it turned out in this game. Not having to worry about the centre allowed White to find good files and squares for his pieces, and then exploit his better pawn structure to win the ending.


Vachier-Lagrave,Maxime - Nepomniachtchi,Ian [C18]
Tournament (7.2), 25.03.2020