A Defensive Proc is a type of proc that has a chance to trigger anytime a particular character is the target of a round of melee combat.
Mechanics[]
Defensive procs are designed to trigger an average of x times per minute, per creature that is attacking. As such, they will tend to proc about the same number of times per minute against any foe, regardless of whether that foe's attack speed is (and whether it is slowed or not).
The number of procs per minute can, however, be increased by having the affected character tank more foes at one time. This fact makes buffs that provide defensive procs very desirable in swarm tanking strategies, where they can be used to dispense large amounts of healing, damage, or debuffing automatically.
Most buffs that provide defensive procs have a limited number of usage counters, which limit how many times the proc can trigger in total before the associated buff fades. As such, when a very large number of foes is being tanked, a defensive proc buff may need to be reapplied multiple times in the same fight in order to continue receiving its effects.
Uncertainty about how long a defensive proc buff will actually last can make it a possible candidate for an audio trigger.