Combat in WoW follows a somewhat unintuitive system known as the Hit Table in order to generate largely intuitive results. As a practical rule, this means that anyone casually using the system will understand perfectly well what occurs, but people who are just starting to understand how it works tend to greatly misunderstand the rules under which it operates.
This article will present both a general overview of the Hit Table as well as the mechanics behind it, and should be suitable for both intermediate and advanced players.
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(Note: All examples used assume the game uses a 100sided die or equivalent; in actuality, the game rolls a number that is at least as accurate as 09999 (for fourdigit results), but these examples are easier to read.
Every time you cast an offensive spell, use a special attack or even just autoattack with a melee weapon, WoW uses the hit table to determine the results of the attack. Instead of performing a roll for each possible outcome, the game will roll one die and then see what that number means in terms of results. Newcomers to the system tend to believe that the system works as a variation on the following;
Alice attacks Bob with her +1 Sword of Smiting. Bob has a 10% chance to dodge the attack, a 5% chance to parry the attack, and Alice has a 5% chance to flatout miss the attack. The game will roll three results; if the game rolls a 10 or lower on the first roll, Bob dodges. If it rolls a 5 or lower on the second roll, Bob parries. If it rolls a 5 or lower on the third roll, Alice misses. If all three rolls succeed, Alice connects with her attack.
In fact, what the game does is compile all possible results of the attack into a single list, and then rolls the die once.
Result  % Chance  Dice Roll 

Miss  5  15 
Dodge  10  615 
Parry  5  1620 
Glancing Blow  0  
Block  0  
Critical  0  
Crushing Blow  0  
Hit  Rest (80)  21100 
This leads to some major divergences from a multipleroll system. Some of the more important include;
I have yet to include critical hits in the attack table because they are something of a special case for the attack table, depending upon what kind of attack you're using. For any special attack that appears in yellow damage (including spells and physical special attacks) the chance to crit is rolled once the attack has been confirmed to land, turning the attack table into a tworoll system. For any damage that shows up in white (melee and hunter autoattacks/autoshot), the chance to crit is included in the original table and there is only a single roll performed.
Result  % Chance  Dice Roll 

Miss  5  15 
Dodge  0  
Parry  0  
Glancing Blow  0  
Block  0  
Critical  0  
Crushing Blow  0  
Hit  Rest (95)  6100 
After his first spell goes off, assuming it doesn't miss outright, the game then rolls once more to determine if it crits. As a practical matter, this means that if your opponent has sufficient evasion (or your miss chance is high enough) your chance to crit will be significantly lower than the critical strike chance on your character sheet.
Result  % Chance  Dice Roll 

Miss  5  15 
Dodge  65  670 
Parry  0  
Glancing Blow  0  
Block  0  
Critical  30  71100 
Crushing Blow  0  
Hit  Rest (0) 
One of the most useful implications of the attack table is the potential to push certain (undesirable) results off the attack table; the most common implementation of this is a Warrior using Shield Block to prevent Crushing Blows from boss mobs.
Result  % Chance  Dice Roll 

Miss  10  110 
Dodge  20  1130 
Parry  15  3145 
Glancing Blow  0  
Block  15  5660 
Critical  0  
Crushing Blow  15  6175 
Hit  Rest (25)  76100 
Result  % Chance  Dice Roll 

Miss  10  110 
Dodge  20  1130 
Parry  15  3145 
Glancing Blow  0  
Block  80  56100 
Critical  0  
Crushing Blow  15  
Hit  Rest (0) 
The potential attacks are evaluated in the order of Miss, Dodge, Parry, Glancing Blow, Block, Critical Hit, Crushing Blow, Normal Hit. No one table uses all of these potential results, of course; Glancing Blows are exclusive to players attacking mobs, and Crushing Blows are exclusive to mobs attacking players, but select the applicable results when calculating a table and in this order. This is only relevant when there are enough results to start pushing potential events off the table.
Players attacking a mob three levels above them will have a 25% chance for the attack to be a glancing blow. Mobs attacking a player three levels below them will have a 15% chance for the attack to be a crushing blow. For more details on these calculations, check their individual articles.
For melee attackers swinging from behind, the rules are different for players and mobs. Mobs lose their parry and block events when attacked from behind; players lose their parry, block and dodge events when attacked from behind.
Ranged attacks can only miss, be blocked, crit or hit. They cannot glance, be dodged or parried.
