What is a Block?
Where dodge and parry are damage avoidance (you avoid the entire effect of an attack), a block is mitigation (you avoid some of the effect of an attack). You have a chance to block, just like you have a chance to dodge and parry, and your chance to block can be increased by effects from items (Equip: Increases your block rating by 23) or by increasing your defense skill (+0.04% chance to block for each point of defense). Any time you are attacked, your chance to block is included in the combat table the mob has against you. If the number comes up as a a block, then you block. Simple! You can see your chance to block by hovering over the block icon in your abilities book. Also note that you can only block physical damage, not elemental (fire, arcane, frost, etc.) damage. As an example, using a shield against Baron Geddon is completely useless unless your shield gives you fire resistance, because all of his attacks are pure fire damage.
Block Value? Block Rating?
Block Value: How much you block for.
Block Rating: Your chance to block an attack. As always, a rating converts into a game mechanic number. In the case of blocking, divide your block rating by X to get how much chance to block that translates into. At level 80 that's 16.4, so if you have 100 block rating, that adds 6.10% chance to block at level 80.
So What's My Block Value?
Mouse over your Block chance in the character window and it'll be in the tooltip.
How Does it Work?
When you block, your block value is subtracted from the damage you would have taken from the attack. Suppose you have 60% mitigation and the block value above. An attack of 1000 damage would be mitigated to 400 damage by your armour. If you don't block, you will take 400 damage (and your combat log reads Mob hits you for 400 damage). If you do block, you will take 278 damage, and your combat log will read Mob hits you for 278 damage. (122 blocked)
If you block an attack where your block value is greater than or equal to the amount of damage, you get a full block. So, if some mob would hit you for 85 damage and you get a block on the attack you would see in your combat log: Mob attacks. You block., and you take no damage from the attack. It used to be that if you got a block against a special attack such as Mortal Strike or the like, it would be a full block no matter how much damage the attack was was for. This was changed quite a long time ago and is no longer the case.
Also remember that your block value translates directly into Shield Slam damage. Shield slam is your biggest threat generating ability, even if it may not be your most rage-effective one (though Sword and Board fixes that up nicely). Other tidbits about Shield Slam:
Diminishing Returns on Offensive Shield Abilities
- 1 block value adds 1 to Shield Slam damage
- Shield Slam crits as per your melee crit chance (plus 5% if you take Critical Block)
- Shield Slam crits are double damage
- One handed weapon specialisation applies to Shield Slam
- Shield Mastery applies to your Shield Slam damage
- Impale, Enrage, and Deathwish apply to Shield Slam
- Shield Slam damage is mitigated by armour
Starting with WoW 3.2, the contribution of block value to the damage done by Warrior Shield Slam and Paladin Shield of the Righteous has diminishing returns. These diminishing returns begin at 30 times your level (2400 block value for a level 80), and there is a hard cap of 34.5 times your level (2760 for level 80). If you have more block value than the cap, then it is not used to determine your shield slam damage. Block value gained from strength, itemised on gear, and gained through items such as block value trinkets all seem to be affected by the diminishing returns. Increases to block value through abilities and talents do not seem to be affected by the diminishing returns (i.e. you will still get pretty good Shield Clam crits with Shield Block up.)
These diminishing returns DO NOT affect how much incoming damage you can block in any way.
The Shield Block Ability
The Shield Block ability gives you a buff that increases your chance to block and your block value by 100% for 10 seconds.
Do I Need 25% Block?
Why are you worrying about crushing blows anymore? The answer is still no.
Can I Block Critical Hits?
Short answer: In PvE you don't block critical hits. In PvP you can.
In PvE, the block, critical hit, and crushing blow entries on the combat table are independent entries. When the random number is generated, the result has to be one or the other or the other. A great deal of parsed combat data from a lot of players supports this, showing that no critical hit from a mob has been blocked by a player. If you've got a screenshot of you blocking a critical hit dealt by a mob, we really want to see it! (email it to me please)
In PvP, the case is definitely different, as shown by numerous screenshots. Right off the top, when a rogue with Cold Blood active hits a warrior with Shield Block active, the hit must be a critical hit because of how Cold Blood works, and it's extremely likely that the hit will be blocked given how Shield Block works. So, we see a blocked critical hit. Beyond that, what we are seeing in screenshots and parsed combat logs is that any white damage attack that is a critical hit cannot be blocked as well, just as in PvE. On the other hand, yellow damage attacks (heroic strike, backstab, mortal strike, etc.) that are critical hits can be blocked - and this is what we have people showing screenshots of. People on the Elitist Jerks forums have some parsing evidence that supports a two table model for yellow damage attacks in PVP. Still haven't seen anyone provide a screenshot of a white damage crit being blocked, but if you have one, please email me!