it's really situational, there are too many factors to give one straight answer. Sometimes, wins aren't determined by direct results but rather the intended results of your actions. I'll list the answer to the first two and then some other conditions that have historically been used.
For clean fights. the clan that dominated the majority of the fight wins (+10-ish opts at all times). if you can't bring the fight back to even after at least 30 minutes, sucks to suck.
For a fight that's devolved into a rag war, if the clan who started the rag war runs away/logs out, they lost.
For when a clan is on the losing end of a fight and trying to regain opts - pulling the fight to a different location and bringing the fight back to matched/plus opts, the clan that was losing can take a dub if they so decide not to follow the clan that was winning when they need to drag to a return spot.
After all, they blew their lead and overextended themselves.
For when your fight is crashed (particularly by a rival) and they have to haul ass to either singles or a return spot 20 minimaps away.
Where you repeatedly crash your rival clans fights with other clans purely with the intention of dropping their opts, leaving and coming back to further hinder their fight.
The goal isn't to 'win' the fight but rather to show that there's nothing your rival can do about it.
Crashing your rival when they're not near a return spot and low opts/inventory forcing them to run away from you - then leaving when their clan is running across the map trying to regain opts.
Again, not an outright clear but if they allowed themselves to be put into a position where they're so vulnerable to their rival that they can't fight back while regaining opts and they didn't pay attention to their rivals actions before getting crashed, that's a failure of their leadership.
If you get hit in single and remain in single when the clan that instigated the singles fight runs into multi - sucks for them, they wanted the singles fight.
That's all I can think of at the moment, however for some reason the present era of the pure community doesn't do a lot of these things. This was all common pre-eoc, as well as up until at least 2016/2017. The fact the pure community has attempted to mimic the main communitys idiotic 'rules' has resulted in the same level of pointless stagnation where every fight is a suicide fest between alliances.