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.
A player, 7 January 2011
When does the reaction of Yoritomo Joben trigger from performing Ambush? Before or after the battle?
Yoritomo Joben
Reaction: Even if Joben is bowed, after the resolution of an action he performed: Straighten him.
Ambush
Limited: Target your unbowed Personality: Create a battlefield (not at any province). Assign your Personality's unit to attack there. Assign another player’s target unit to defend there, even if its Personality is bowed. Other units will not move there. Fight a battle there (after this action's resolution). After the battle ends, lose 5 Honor.
Zen Faulkes (rules official), 7 January 2011
When does the reaction of Yoritomo Joben trigger from performing Ambush? Before or after the battle?
http://rules.l5r.com/CE_Effects#Order_of_effects: "Battles created by effects, and additional phases, segments, and actions granted by effects, are delayed until the action or triggered trait that granted them has ended, and the chance to take Reactions to the end of the action or trait has passed." Emphasis added.
Before.