Druids, Focuses, Shields, and Spells involving a weapon

Question

One of my players has a 2nd level Druid. He’s been casting shillelagh on his club, he’s also using a shield. I’ve been a little loose with the Druidic focus mechanics but I desire to be more precise in accordance with RAW. My question is essentially about holding an focus in one hand and having a magical effect occur in the same hand. If he dropped the shield then the question would be moot, but he likes the +2 to AC.

With Shillelagh, the club or quarter staff needs to be one that “you are holding” so you couldn’t cast it while using a shield. But what if the club or quarter staff was also a Druidic focus? I am not aware of any information about using a focus to cast a spell on itself.

How about a spell like Flame Blade? “You evoke a fiery blade in your free hand.” Discussing the exact nature of the focus with my player, one idea is that it’s a talisman or totem hanging on a long necklace... fending off a rain of arrows with his shield, he raises the talisman in his free hand and evokes Flame Blade, which appears in his free hand at the moment he drops the talisman which conveniently falls back in place hanging from the necklace. Or something like that.

According to rules from PHB regarding a focus and specific spells, it seems unlikely that either of these examples are allowable... however they are so CLOSE in my view to making sense that I figured others may have come across this situation and found a clarification on it. I have searched online here and elsewhere and while I may have missed something, I haven’t found an answer. I was hoping someone might know of some relevant information that could definitively answer this question one way or the other.

Thanks for looking—hopefully my questions make sense.

Answer 1

I feel like this question has been covered in parts before. I've included references. These answers quote Mike Mearls and he says yes you can use of a staff as a focus. You'd likely need permission from your DM to use a club as a focus.

DMG page 140 says that a staff can be used as a quarterstaff.

If you have your focus/weapon in one hand your other hand is free to hold your shield. That too is covered below, but if in doubt War Caster definitely allows a caster to hold a weapon and a shield.

Druidic Focus. A druidic focus might be a sprig of mistletoe or holly, a wand or scepter made of yew or another special wood, a staff drawn whole out of a living tree, or a totem object incorporating feathers, fur, bones, and teeth from sacred animals. Covered here

Using a staff as a weapon and a focus has been covered here.