The description of the produce flame cantrip reads:
A flickering flame appears in your hand. The flame remains there for the duration and harms neither you nor your equipment. The flame sheds bright light in a 10-foot radius and dim light for an additional 10 feet. The spell ends if you dismiss it as an action or if you cast it again.
You can also attack with the flame, although doing so ends the spell. When you cast this spell, or as an action on a later turn, you can hurl the flame at a creature within 30 feet of you. Make a ranged spell attack. On a hit, the target takes 1d8 fire damage.
If I have one hand occupied with a shield and another hand occupied with an arcane focus, can I cast produce flame into one of my occupied hands?
If I have the War Caster feat, can I then use the flame as an opportunity attack while my hands are occupied?
I'm getting ready for a one-shot battle-royale and want to be able to have a free damage cantrip.
This question is different from the question Can you cast and hold Produce Flame and then wield a weapon and shield?. The previous question is about casting produce flame with an open hand and then equipping an item. I am specifically talking about having both hands equipped with items and then choosing to cast produce flame.
Best Answer
Normally, you could not cast it at all with no free hands- the spell has V, S components, which means you need an empty hand to perform the somatic components, even if one of the hands is holding a focus.
However, the War Caster feat exists. So what happens when you cast it with full hands in that scenario?
Well, the spell says the flame appears in your hand and doesn't hurt you or your equipment. It also says it remains there for the duration, and lists the ways the spell can end. Since the spell effectively states the flame remains in your hand until the spell ends or the flame is hurled, I think the magical flame is in no danger of being doused, smothered, or dropped just because something else is in your hand- the spell doesn't allow for that in its text.
You should be safe to continue holding your equipment in-hand, and the flame will continue to co-exist/(safely) burn around it.
As far as an opportunity attack via War Caster goes, War Caster only adds the ability to cast a spell as a reaction as an alternative to the usual opportunity attack. RAW, I believe it would allow you to newly cast produce flame and then immediately attack with it ("When you cast this spell, [...] you can hurl the flame at a creature within 30 feet of you"), but wouldn't allow throwing a previously-prepared instance already in your hand- not that it matters, you could just cast it anew instead for no real difference.
Do note that using the War Caster reaction to attack with the spell would result in attacking with disadvantage, as the target would still be within 5 feet of you when you made the ranged spell attack.