25. When a Cannon is attacking an unprotected Knight, Guard, Minister, or Pawn that has crossed the river, it will be a perpetual chase even if only the cannon mount moves but neither the attacking Cannon nor the attacked piece moves.
However, perpetually chasing a Pawn that has NOT crossed the river is allowed. (See examples in Diagram 56 to 60)

Diagram 56: Red (in Capital) moves first

P12 c58
P23 c87
P32 c78
P23 c85
P32 ...

Explanation:

The Black Knight is not protected and cannot be perpetually chased. The Red Cannon uses different mounts to attack the Black knight and is perpetually chasing the Black Knight. Red has to change.

Diagram 57: Red (in Capital) moves first

C34 c96
g4-5 c68
g5+4 c96
G4-5 c68
G5+5 c86
G4-5 c68
G5+4 ...

Diagram 58: Red (in Capital) moves first

C43 c76
M1+3 c67
M3-1 c78
M5+3 c87
M3-5 ...

Explanation:

In Diagrams 57 and 58, the Red Cannon keeps chasing the Black Guard or Minister by changing its mounts. Red violates the rule and has to change.

Diagram 59: Red (in Capital) moves first

M3+1 c79
M1+3 c96
M3-1 c69
M1+3 c96
M3-1 ...

Explanation:

The Red Cannon perpetually chases the Black Pawn by changing its mounts. Because the Black Pawn has crossed the river, Red violates the rule and has to change.

Diagram 60: Red (in Capital) moves first

M3+1 c79
M1+3 c96
M3-1 c69
M1+3 c96
M3-1 ...

Explanation:

Although Red perpetually chases the Black Pawn, which is unprotected, by changing its mounts, because the Black Pawn has not crossed the river this does not violate the rule and the game should be ruled a draw.