From Diablo Wiki
Blocking is a property granted by the use of a shield, or by other items or weapons, in rare situations.
Blocking works very differently in Diablo III than in past games in the series. In D3, blocking is basically an item based form of absorb, reducing the physical damage of attacks by a set amount, one based on the shield being used and potentially modified by skills or traits. This has the effect of making shields much less protective than they were in Diablo II, when any character could eliminate up to 75% of all incoming physical damage with the use of a shield.
A successful block in Diablo III is calculated much as it was in Diablo II, with the character's dexterity and equipment checked against the attack rating of the enemy. Presumably blocking will not work while running in Diablo III, though this is not confirmed.
Shields in Diablo III
The stats of a Buckler as seen in August 2010.
- Armor: 78
- Chance to Block: +25%
- Block Amount: 6-10
- Durability: 25/25
- Sell value: 1
This item is presumed to be part of the Barbarian's starting equipment, since the sell value is just 1.
See the shields article for much more detail.