But I want to look at that closely...
I agree with Chris Hogan's comment that "Shields Shall Be Splintered" can only be used once per round, and furthermore a fighter pulling a new shield from a bag of holding is neither attacking nor defending for one round. When facing a single opponent, the fighter with a bag of holding can only avoid damage every other round; when facing multiple opponents, the advantage is significantly less. The fighter with shield bearers -- which did exist historically, btw -- likewise can't attack or defend while taking a shield from the shield bearer; plus, shield bearers cost money, are vulnerable to attacks, might choose to flee from combat, and should be subject to the command control rules from U&WA, so it might take a couple rounds to get that replacement shield, even when everything else goes well.
On top of that, you have to make a decision what it means to skip defending yourself for a round. When a fighter stops to take a shield from a bag of holding or a shield bearer, or for that matter stops to switch weapons, drink a potion, or do anything else, how do you resolve attacks on the defenseless fighter? I see a couple options:
- No Change: Fighter might lose the benefit of a shield, but otherwise continue to defend with normal AC. Successful attack may interrupt action or force fighter to drop item.
- Penalty: As above, but fighter is slightly easier to hit; usual numbers cited are +2 or +4 to attack defenseless opponent.
- Vulnerability: Fighter's AC is effectively 9 (no armor) because opponents can now target weak points like eyeslits easily.
- Truly Defenseless: No attack roll necessary, just roll for damage.
- Helpless: Identical to attacks against sleeping or bound opponents (i.e. instant death.)
I haven't decided, but I'm leaning towards #s 3 or 4. At the very least, an attack on a fighter who isn't defending should include the possibility of interrupting or disarming the fighter as per #1, but #1 seems unusually weak to me. Anything stronger than #1 seems to make Supreme Thousand-Shield Defense not very viable as something to do in combat.
And this isn't even considering damage. Should "Shields Shall Be Splintered" block any amount of damage, or just the damage that would be done by a weapon of equivalent size (1d6 for us "d6-only damage" users.) Adopting a rule like that would prevent the supposed ordinary fighter avoiding damage from giants example.