Active blocking

Player characters can actively block by holding the block key (default: left shift). While blocking, a character gains +2 Armor Class, has increased Damage Reduction, and is immune to most special attack and weapon effects. This includes, but is not limited to, Scorpion/Spider Poison, Wraith Constitution Drain, and damage enchantments such as Crippling, Flaming, Wounding, Maladroit, and even Bane. Active blocking to dodge special attacks requires a fast internet connection and player dexterity.

A shield is not required to actively block, although blocking with a shield provides significantly more bonus DR than blocking without one. All benefits mentioned above apply regardless of the character's equipment. A player can block and gain its benefits even while prone.

Implications
The benefits of blocking apply only to melee attacks against the character's front 180°. Against ranged attacks, the bonus DR from active blocking, as well the various immunities it bestows, apply to attacks from all directions, but you will only receive half your normal total DR than you do against melee strikes.

A blocking character cannot attack with weapons. If he has a shield, he may attack with it instead, using the shield's attack and damage values. This requires no special skill or feat, though the character suffers attack penalties if he is not proficient with that shield, and he loses the shield's bonus to his Armor Class unless he has the Improved Shield Bash feat.

Characters cannot run normally while blocking. They either hop or somersault instead, depending on their Tumble skill. Blocking characters cannot jump at all. Blocking characters can cast spells and activate items, but this cancels the blocking status until the casting finishes.

You can block while helpless.

Active damage reduction
Active DR is the additional Damage Reduction gained while blocking. It stacks with the character's Passive DR.

Note: Thrown weapons and wands are treated as one-handed weapons in these categories.

With shield
This formula applies when blocking with a shield, regardless of what's in your main hand.

Active Melee DR = (BAB / 2) + 2 + Shield DR rating + Shield Mastery Enhancements

Active Ranged DR = Active Melee DR / 2

The following enhancements may be taken to increase Active DR while using a shield.
 * Dwarven shield mastery +1, 2, or 3 (for levels I, II, and III of the enhancement)

Two weapon fighting, bow, or crossbow
This formula applies when blocking while wielding two one-handed weapons or a bow or crossbow.

Active Melee DR = (BAB / 3) + 2 + Two Weapon Blocking Feat (two weapon fighting only)

Active Ranged DR = Active Melee DR / 4

The following feat may be taken to increase Active DR while wielding two weapons.
 * Two Weapon Blocking

Two-handed fighting, single weapon without shield, or unarmed
This formula applies when blocking while wielding a two-handed weapon, wielding one one-handed weapon but no shield, or fighting unarmed.

Active Melee DR = (BAB / 5) + 1

Active Ranged DR = full Active Melee DR

Examples
Example 1 - A level 8 fighter with the regular and Improved shield mastery feats, actively blocking with a +4 Heavy Adamantine Shield would have the following DR when using or blocking with shield:
 * Passive DR vs. melee and ranged = DR1/-
 * Active Blocking DR vs. melee = 1 + [(8/2) + 2 + 2 + 4 + 6] = DR19/-
 * Active Blocking DR vs. ranged = 1 + [(8/2) + 2 + 2 + 4 + 6]/2 = DR10/-

Example 2 - The same level 8 fighter with two weapons would have the following DR:
 * Passive DR vs. melee and ranged = none
 * Active Blocking DR vs. melee = [(8/3) + 2] = DR4/-
 * Active Blocking DR vs. ranged = [(8/3) + 2]/4 = DR1/-

Example 3 - A level 14 barbarian with innate DR5/-, a two-handed weapon (THF), and Stoneskin (DR10/Adamantine) would have the following DR:
 * Passive DR vs. melee and ranged = DR10/Adamantine OR DR5/-For normal attacks he effectively has DR10. For Adamantine attacks he has DR5/-.
 * Active Blocking DR vs. melee and ranged = [10 or 5] + [(14/5) + 1] = DR10/Adamantine OR DR5/- AND DR3/-For normal attacks he effectively has DR13. For Adamantine attacks he has DR8/-.