Is there any official ruling on this mechanic?
Whenever the samurai defeats the target of his challenge, he regains one daily use of his resolve, up to his maximum number of uses per day. Defeating the target of his challenge usually involves reducing the target to 0 hit points or fewer, but the GM might rule that an enemy who surrenders or flees the battle is also defeated.
My local GMs are also struggling with the interpretation of this statement. It's vague as to what it really means by the word "defeat". There are other classes with a similar mechanic that the wording is very clear.
For example, Gunslinger is very specific about regaining Grit when it says, "When the gunslinger reduces a creature to 0 or fewer hit points with a firearm attack while in the heat of combat, she regains 1 grit point." This explanation is very specific to how it's done and that's "with a firearm attack".
Samurai resolve is very ambiguous because it says "defeat". Then it explains what "defeat" usually is, but not that it has to be done specifically by the samurai, just that it has to be done. However, the statement that follows, "but the GM might rule that an enemy who surrenders or flees the battle is also defeated", seems to refer to a party situation. A samurai wouldn't typically force a surrender or flee on his own as he would be amongst his party most of the time.
If it's ruled to work like Gunslinger Grit, then that's fine. I would find it very limiting though as this is the only way to recover Resolve and it requires the use of a second skill, both of which are limited by character level. Grit points can be increased by other means besides level and regained by other means besides reducing an enemy to 0 hp.
