19. When a Rook cannot move because of an opponent's Knight, the Rook cannot be perpetually chased, regardless of whether the opponent's Knight is protected. (See examples in Diagram 39, 40, and 41)

Diagram 39: Red (in Capital) moves first

R8+2 g6+5
R8-3 g5-6
R8+3 g6+5
R8-2 g5-6
R8+2 ....
.

Diagram 40: Red (in Capital) moves first

C8-1 g5-6
C8-1 g6+5
c8+1 g5-6
c8-5 g6+5
c8+5 ....
.

Diagram 41: Red (in Capital) moves first

N9+8 g6+5
N8-7 g5-6
N7+6 g6+5
N6-7 g5-6
N7+8 ....

Explanation:

In Diagrams 39, 40, and 41, the Red Knight is not protected but because the Black Rook doesn't move, it is not considered as a perpetual chase. On the contrary, each of the Red moves attacks the Black Rook and this is a violation of the rule. Red has to change.