[Righteous Defense is a Taunt] ability that defies all regular threat abilities and is regularly used by tanks. It does three things:
You gain as much threat as the person currently holding aggo
It gives you aggro
It forces the NPC to attack you for three seconds
Note that the latter two are not the same thing. A third person could get 110% of your threat during the first three seconds and not recieve aggro due to the taunt debuff on the target. However, when that time expires, it grabs aggro as usual.
(Credit: Lavina, The Venture Co.)
SPELL HIT AND TAUNTING
A brief note about Spell Hit with regards to Righteous Defense (Taunt):
Q u o t e:
Taunt falls under the rules of Spell Resistance. For the purposes of this game, if there are any critical Taunt fights such as the Four Horsemen of Naxxramas, getting 5% Spell Hit will minimize the chance of resists.
(credit: Ciderhelm, Cenarius)
In this way, it is subject to the same Miss Chance Formula as an actual attack. A “missed” spell comes up as a “Resist”.
It is not necessary to stack Spell Hit under normal circumstances, unless it is a very, very precise, Taunt-dependant encounter. Simply be aware of the mechanic.