Hawk Eye - What's consider vulnerable target?

siuolly

As the title state, what's consider vulnerable target? I only able to find a brief mentioned in this Ask anything combat (http://elderscrollsonline.com/en-uk/news/post/2013/03/08/ask-us-anything-combat) but still have no clue what's consider a vulnerable target. Anyone?

Barthalas

I'm relatively sure it means when the target is affected by an armor-reducing effect (visible by the "shattered" HP bar), applied by the first 1h/shield ability, weapon enchantments or the set that reduces armor by 20% on critical hits.

It's either that or the brief stance enemies enter when you block/interrupt them.
If it's the first it's really OP in comparison to other weapon passives. If it's the latter it's really useless in comparison to other weapon passives.