Complex sentence: If the player completes a two-square king move without touching a rook, he must move the correct rook accordingly if castling in that direction is legal, otherwise the move must be withdrawn and another king move made.
Split into simpler sentences: If the player completes a two-square king move without touching a rook, he or she must move the correct rook accordingly if castling in that direction is legal. Otherwise, the move must be withdrawn and another king move made.