@fmacanadaguy @JeremyECrawford I've run it as yes
— Mike Mearls (@mikemearls) April 28, 2016
@G0DL1K3D3V1LSorry if this is a late question, but if said character also has Warcaster, can he cast a Warcaster legal spell? War Caster does, indeed, work with opportunity attacks, as specified in its third benefit.
— Jeremy Crawford (@JeremyECrawford) March 6, 2017
I thought if a creature is moved involuntarily then opportunity attacks do not apply. Since the creature is affected by a spell that makes it move then how is it open to the attack?
The ruling (per the books and SA responses elsewhere) is that a creature moving doesn’t invoke an OA *if* the creature didn’t employ its Movement, Action, Bonus Action (relative to those who can for such purposes, like rogues) or Reaction in order to do so. Examples of it not applying: character is pushed back by Thunderwave or similar effect, or a knockback feature included in a creature’s attack, etc. Example of where it does: Dissonant Whispers, as the target must use their Reaction *if available* (key point there — it the target doesn’t at that instance have its Reaction available, it doesn’t move as a result) to move away from the caster, direction-wise. Other examples of that are indicated in some other spells or similar effects.