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.
This is in reference to viewtopic.php?f=59&t=88238&p=1168332&hilit=joben#p1168332
I understand that the reaction occurs before the battle. However, I'm still a bit confused by the timing. My questions all boil down to this:
Can a bowed Joben perform Ambush? I would think not, but there are some folks who disagree.
However, I'm still a bit confused by the timing.
Yoritomo Joben's Reaction would straighten him "after the resolution of an action he performed" (card text). The action's resolution takes place after its mandatory costs are paid, which happens after its explicit performers and required targets are chosen (see Abilities and actions).
Can a bowed Joben perform Ambush?
No, because Ambush requires an unbowed performer, so Joben needs to be unbowed when Ambush would target him. It does not matter that his Reaction would straighten him after Ambush resolves and before the battle begins.