Figure[White to move]

Does White have a pin in place here? Almost, but not quite. Consider each of his pieces and you can see that his queen seems to pin Black’s rook to Black’s queen, but that the Black queen has protection; so if the Black rook moves, the most White can do is exchange queens. The position would be quite different if Black’s queen were loose, and this White can achieve by going after its guard. White takes it with BxN; after Black recaptures with b7xN, the exchange has left the queen without a defender—and the rook on d2 pinned, since if it moves White now plays QxQ for free.

All right; the next step is to ask how much force each side can bring to the scene of the paralyzed piece, which currently is attacked once and defended once (by a queen on each side). White plays Rd1, and Black plays Ra8-d8—a standard summoning of rooks by both players. Does White have any other pieces he can use to attack the d2 square? Yes: Bc1. Black is out of defensive pieces, so the rook goes to White.