Tank in pvp-gear

[zenga]

Anything but a druid blows in pvp gear as you simple don't have the mastery / dodge and parry to mitigate the damage. As a pally (not sure for dk or warrior), if an opponent of the same level melee attacks you the following table determines your reaction: (basically the server picks a number between 1 and 100, if it's 14 you'll parry, if it's 1 the boss will miss you, if it's 22 he will crit you)

you have a 5% chance that he will miss (1-5)
you have a 5% chance that you will dodge the attack (6-10)
you have a 5% chance that you will parry the attack (11-15)
you have a 5% chance that you will block the attack (16-20)
you have a 5% chance that you will get crit (20-25)
you have a 75% chance that you will get hit for normal damage (26-100)
(this is for equal level mobs)

if you chose protection you gain 18% block by default through base mastery, and you gain 6% less chance to be critically hit which changes it into:

you have a 5% chance that he will miss (1-5)
you have a 5% chance that you will dodge the attack (6-10)
you have a 5% chance that you will parry the attack (11-15)
you have a 23% chance that you will block the attack (15-38)
you have a 0% chance that you will get crit (you can no longer be critted as a tank)
you have a 62% chance that you will get hit for normal damage (39-100)

the idea is that you - by acquiring parry/dodge & mastery) want to reduce the chance you'll get hit, say you gain from gear 10% parry, 10% dodge, 40% mastery than it would look like

you have a 5% chance that he will miss (1-5)
you have a 15% chance that you will dodge the attack (6-20)
you have a 15% chance that you will parry the attack (21-35)
you have a 63% chance that you will block the attack (36-98)
you have a 0% chance that you will get crit (
you have a 2% chance that you will get hit for normal damage (98-100)

So once you reach 100% (102.4% vs a raid boss due to level difference) you are block capped. In my exampled it could come from 2% extra block, so in that case you'd have a 35% chance to avoid the attack and a 65% to block it (block changed btw since wotlk, it's basically an absorb).

Just wanted to point out why it's so important to get these tank stats, unless your healer overgears the content. And from the 3 new heroic dungeons you can get block capped for raid bosses.

Edit: btw parry & dodge share diminishing returns, so mastery is far more favourable for tanks (prot warrior, pally & dk), and together with agi/crit for druids as well (though not too sure about bears)