Why does Clemency get interrupted? And why does Sword/Shield Oath reset combo?

[Giantbane]

Incoming spike damage pld switches to shield oath, damage is mitigated immediate increase in effective health and effective healing.

Incoming spike damage war switches to defiance, dies as increase in effective health is not immediate.

pld uses a skill to activate his mitigation. Warrior needs to use a skill to benefit from his.

But a war switching to defiance to take spike damage is probably going to be using Inner Beast to mitigate that attack. In which case they'll be restoring some of that missing HP on their own.