Balance is the defensive attribute granted by Armors and Shields allowing entities to resist Staggers from hits.
Poise is the offensive attribute granted by Weapons and combat animations allowing entities to cause Staggers from hits.
Every attack that hits subtracts from the defender's Balance. When this Balance is reduced to 0 or less the defender enters a second soft-stagger lasting approximately 0.1 seconds. This soft-stagger interrupts the current action and restricts players from rolling. After a soft-stagger Balance is reset to 100% of its normal value.
Balance can be gained by wearing medium and heavy armors. Armors granting 20 Balance can only sustain 10 Poise damage. I.e. Balance from armors is halved in the calculation.
Shields also have a Balance value. In game this is listed as Stagger Reduction. Shield balance is a percentage reduction to Poise damage and reduces Poise damage when blocking. Shield and armor Balances stack multiplicatively, but only stack together while blocking.
When blocking, Balance controls the amount of Stamina the player loses with Poise damage instead of soft-stagger, a full Stagger is received when the player runs out of stamina.
The formula for Balance when blocking is given as:
100% - (Shield_Percent + (100% - Shield_Percent) * (Balance / (Balance + 40)))
An armor's Balance cannot be increased with upgrading, but a shield's Stagger Resist % can be upgraded. The formula for upgrading Stagger Reduction follows the same format of armor/shield upgrades: Value * (1.10^Rank)