In order to play Opposing Rook, the player's bishop must be moved from its starting position (88 or 22 squares).
[a] Opposing Rook games played by White are usually triggered by this move.
White prevents the pawn trade by moving their bishop to the third file defending the 24 square.
This move also clears a path for White's rook to swing over to the second file early.
At this point, White has the option of immediately swinging their rook to the second file allowing their king to start castling.
Alternately, White can delay the rook and instead start moving their left silver upward to reach the 67 square.