Guards

Guards are effects can trigger when you are a target of a successful attack (they happen on being hit). Few unique guards also proc on being missed. The effects vary.

Proc rate:
 * Some guards trigger with 100% probability (always), some trigger more rarely.
 * Some guards cannot proc again immediately; one must wait x seconds before next proc.

Trigger:
 * Being hit by a melee attack
 * Being hit by ranged attack
 * Being hit by a spell

Target of the guard effect
 * The character being hit
 * The attacker
 * All enemies around defender

Effects are very different:
 * Attackers are usually dealt damage in return (for example ), or are a target of some debilitating effect (Radiance Guard)
 * Defenders usually receive a buff (for example Earthen Guard, temporary HP, or minor heal
 * BUG (confirmed by devs in 2016; still current in June 2019): guard effects on all random loot only deal 1d8 damage, regardless of item level and tooltip. Guard effects on some named items do work correctly.

Sources of guard effects
 * Items
 * Class enhancements (for example Elemental Defense)