"Nobody ever defended anything successfully, there is only attack and attack and attack some more" - Patton
Knowing how to cut support is just as vital as knowing how to give it. Cutting support can disrupt attacks, help you to field agile defenses and save your territories from capture.
A move to cut support can be as effective as a normal defense, and doesn’t require the two units to be next to each other!
The unit being attacked can never disrupt the support of the unit that is attacking….
The first exception to the above rule: If a province is being attacked, the unit there can’t cut the support of a unit that is helping attack it:
Unless the defender manages to dislodge the supporting unit
The exception to the exception. You CAN disrupt the support of an attack against yourself if you dislodge that unit.
A dislodged unit can still cut another unit’s support (going a different direction)
Because the turn is a simultaneous resolution of all actions, units that are dislodged can still cut support of other attacks:
reference rules in full page 11 diagram 18