From Diablo Wiki
Blocking usually refers to the action of blocking an attack with a shield. All physical attacks and some magical ones can be blocked, and a shield is an essential item for many character builds in Diablo II.
Blocking is capped at 75% effectiveness. Any % above 75% is irrelevant. Dexterity raises a character's % chance to block. Some items and skills also increase blocking %.
 Blocking Display
Hover the pointer over the character window to display your character's blocking percentage. This is not always accurate, thanks to the LCS, since some spell bonuses and other special effects are not displayed properly. But it's a fairly accurate read out.
 Defense and blocking
Blocking can also refer to the benefits of your character's defense. Incoming physical attacks check a character's defense rating to see what % chance they have to hit. Ones that fall short of hitting (determined by your defense, the monster's attack rating, and possible magical effects) are in effect "blocked" by your armor.
When defense "blocks" an attack it has no animation and it will not interrupt your attack (or casting). This is different from the Shield block animation or the amazon D/A/E (which will interrupt your attacks even if you don't get the animation)
- See the Defense 101 article for more details.
 Blocking Formula in Diablo 2 Lord of Destruction
Chance to Block (CTB) with a shield is calculated via a straightforward equation based upon only three variables: Your character's level, your dexterity level, and the shield's base blocking percent for your character's class (plus modifers). In equation form:
Total Blocking = (blocking * (dex - 15)) / (cLvl * 2)
- blocking = A total of the blocking on all of your items. Keep in mind that shields with "+x% Increased Chance of Blocking" have already added their bonus to the shield's blocking percentage that you see when hovering over it.
- dex = The character's base dexterity plus all dexterity bonuses (f.ex. charms, equipment)
- cLvl = The character's current level
The result, Total Blocking, is then capped at 75%, meaning that the chance to block cannot be increased above this by any means. This percentage applies to standing still, melee attacking, and walking. Running, however, reduces the chance to 1/3rd of the original value, with a cap of 25% chance to block.
Running Block Chance = 1/3 * Total Blocking
Because equipment plays a crucial role in how much dexterity is required to reach the maximum 75% chance to block, many players calculate their required endgame dexterity based upon their planned endgame gear, not what they are currently wearing (which would usually require more dexterity for a given endgame cLvl).
 Faster Block Rate
A character goes into block animation if its opponent succeeds in the hit check and the character succeeds in a blocking check. The character can do nothing else during the blocking animation. Blocking is only possible while engaged in melee combat, or while walking. (Not while running.) See the blocking article for more details.
Improvements to faster blocking are difficult to achieve since the bonuses to it are found almost exclusively on shields.
- In some cases the equipped weapon influences the blocking speed.
- The Assassin's Weapon Block skill is also affected by her Faster Block Rate, and the same values as for shield blocking apply.
- Act 3 mercenaries do not block even though they are capable of using a shield.
|Character||Weapon / Skill / Form||Block Frames|
|Amazon||1H swinging weapon (*)||0||4||6||11||15||23||29||40||56||80||120||200||480|
|with Holy Shield||0||86|
|Character||Weapon / Skill / Form||17||16||15||14||13||12||11||10||9||8||7||6||5||4||3||2||1|
(*) 1-handed swinging weapons include 1-handed axes, clubs, 1-handed maces, orbs, scepters, 1-handed swords, 2-handed swords wielded in one hand, throwing axes, and wands.