Damage block

Damage block is a mechanic that reduces physical attack damage a unit takes by a flat amount. Most damage block abilities are chance-based and passive.

Mechanics
Damage block reduces any physical damage a unit takes from attacks or from cleave, with the exception of damage dealt by the attacks of ward-type units. Damage block does not trigger against physical spell damage, with the exception of the spells listed below. Unlike armor, damage block reduces a fixed amount of damage, instead of a percentage.

When damage block triggers, it blocks damage before other damage reducing effects do. This means that the higher the unit's armor is, the less effective damage block gets. See final attack damage for the complete calculation.

All chance-based sources of damage block use pseudo-random distribution.

All melee heroes have damage block by default. This damage block works against every non-player unit, and enemy heroes (inlcuding illusions, clones, and creep-heroes), but not against other player-controlled units.

Blocked spell damage
The following spells' damage is blocked by damage block.

1 Only returned/reflected physical damage is blocked. Magical and pure damage is not blocked.

Visual feedback
When a damage block occurs, a ocre-colored negative number pops up on the blocking unit, with a shield icon on the right side of the number. This number shows the exact amount of damage blocked.

Stacking
The proc chances of all sources of Damage Block work independently from each other. However, when multiple Damage Block sources proc on the same attack, only one of them actually blocks damage, the one with higher block values getting prioritised, while the others do nothing. This results in a diminishing stacking behavior. An exception to this is the melee damage block, which fully stacks with other sources of damage block.

Example: When having two, the chance of blocking damage becomes:
 * 1 - ( × ) = %

When having one and one, the chance of blocking damage from hero attacks becomes:
 * chance for Vanguard to proc, and ×  = % chance for Poor Man's Shield to proc

This is because half of the time Poor Man's Shield procs at the same time as Vanguard does, but since Vanguard has the higher block values, Vanguard gets prioritized, effectively negating half of the Poor Man's Shield procs.

Sources of damage block
Every melee hero has a passive damage block that has a 50% chance to block 16 damage of every non-player attack, and every attack from heroes, including illusions, clones and creep-heroes. This damage block does not work against other player-controlled units.