A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
In response to: viewtopic.php?f=59&t=59926&p=769394&hilit=Unexpected+betrayal#p769394
Situation: Doji Bob is a thorn in my side, but dishonored so I Ambush him. I sneak/Unexpected Betrayal, then I get hit with Block Supply Lines, leaving him the only unit in the battle. So I'm assuming A, but I want to check. Which of the following happen:
A) No armies mean no resolution B) Both sides have nonexistant force, making it a Tie, and the Unit dies
A. Compare the total Force of each army. Whichever army has the most Force wins (see Force total). A side with no units has zero force for purposes of this comparison, and does not count as an army for effects that alter the force of an “army”.
The winning army’s leader (the Attacker or Defender) is the winner of the battle.
If both armies have the same Force and both armies contain one or more units, the battle is a tie.
Any other result (such as an army with total unit force of zero versus a side with no units) has no defined outcome.
This is a case of one side having 0 Force and 1 unit vs. another side with no units - and thus has no defined outcome. No one dies, wins, loses, or ties.