I see all shields have a block% and a damage reduction component.
I have 2 Questions:
If an attack proc a block. Is the block damage reduction applied before or after armor and relevant resistance have been applied?
What damage sources are possible to block?
1) Your block is applied after armor/resistances are calculated. Shields would be useless at later difficulty levels if this wasn't the case.
2) You can block any damage, including ranged attacks, magic attacks, AOE attacks, DOTs, etc. In addition, blocking works the same regardless of the direction you're facing or if you're moving or not.
Side note: No stat affects your block chance. What you see on your equipment or on your skills is what you get.
Regarding point #2;
Yes you can block physical melee + ranged attacks, I am unsure about the AOE attacks but I have received blocks while standing in desecration (with nothing else available to attack me) so I can only presume that blocking works in this scenario as well.
Update: I've tested ranged elemental attacks, and these can also be blocked. You can also block while moving and with your back to an enemy.
I agree with ickleislands but would like to put some clarifications.
A shield has two different effects going on at once. There is the increase in armor and the block percentage. The increase in armor is the rather large number with the purpose of decreasing all physical damage. The block percentage is located under the armor rating and it represents the chance that you will successfully block an attack. If this happens, you take no damage for that attack; it is similar to dodging.
Blocking is granted by shields and it works much like resistances and armor do in Diablo III. A shield provides another form of damage mitigation, rather than a way to decrease enemy chance to hit. All shields have a % chance to block, and an amount of damage they will absorb upon a successful block. A character's actual blocking % is determined by the shield's number.
Blocking works very differently in Diablo III than in past games in the series. In Diablo III, blocking is basically an item based form of absorb, reducing the damage of attacks by a set amount, one based on the shield being used and potentially modified by item bonuses. This has the effect of making shields much less protective than they were in Diablo II, when any character could eliminate up to 75% of all incoming physical damage with the use of a shield.
A successful block in Diablo III is calculated much as it was in Diablo II, with the character's equipment checked against the attack rating of the enemy.
As resistances provide another form of damage mitigation, one tailored to individual types of magical damage. The biggest change to resistances in Diablo III is that they are no longer percentage-based. They are instead like armor; a number that increases with item and skill bonuses. The higher the number, the more damage they absorb.
This means that characters can always benefit from more resistance, rather than the value capping off at 75%. (Items that add to maximum possible resistance are not found in Diablo III.)
