Description: Gives a chance to block enemy melee and ranged attacks.
The ability of a shield to absorb melee damage in addition to its armor value. When a shield is equipped, you have a certain chance to perform a Block. The basic chance to block an attack is indicated on your character sheet under the Defense tab. This value assumes that you fight against a mob or other character of same level. Fighting a mob of higher level than yourself decreases your chance to Block, and vice versa.
Your base chance to block an attack is 5% and this is modified by a factor of the rating difference between the attacker's weapon skill and the defender's defense and block rating. Each point of difference adjusts the base chance by 0.1% if the target is a mob and 0.04% if the target is a player. Mobs level 9 and lower do not block as frequently, just as they are not missed as frequently as they should be. Also, mobs cannot block more than 5% of attacks regardless of rating difference.
The amount of damage a Block reduces depends on the block value of your shield, any enchantments, talents and your Strength. Damage reduced by blocking is calculated after other damage reducing factors, such as armor, which increases the effectiveness of blocking.
Defense against Critical Hits and Crushing BlowsEdit
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Paladins and Warriors have abilities to greatly increase their block chance for a short while. The primary purpose of these abilities is to allow the sum of Avoidance—the mob's miss chance, and your dodge and parry chance—and Block to exceed a certain percentage that is related to the relative level of tha attacker (102.4% for a level 73 "boss" against a level 70 player). By doing this, any chance of the mob scoring an unmitigated hit, critical, or crushing blow is pushed right off the table and becomes 0%. This is especially useful when tanking bosses or other hard-hitting mobs.
Negating critical hits and crushing blows increases the actual mitigation immensely and is why using a shield is considered a must for all tanks.
The fact that a Block may only mitigate damage partly—which means the enemy's attack speed and damage per attack becomes a factor—and the fact that the talents increasing Block chance cannot reliably be active at all times, makes it harder to calculate the actual benefit of Block in comparison to other damage mitigation mechanics, such as armor or chance to get missed.
While it is clear that a Blocked attack made against a player cannot be a crit, it is possible that mobs have different rules for determining whether an incoming attack is blocked or not, which includes the possibility of a "blocked crit".
It should be noted, however, that only special attacks—i.e. yellow-damage instant attacks such as Claw, Overpower, and Sinister Strike, and yellow-damage on-next-swing attacks such as Heroic Strike and Raptor Strike—have been observed as inflicting blocked crits. Normal white-damage auto-attacks have never been seen inflicting a blocked crit, and are probably subject to the same mutually-exclusive-attack-result rules that attacks made against players are.
Note too, that unlike player characters, mobs sometimes block attacks even though they have no shield equipped.