A critical strike is a basic attack or an ability that deals more damage than usual.
Critical strike chance
Champions and units have a base critical strike chance of 25%. Critical strike chance cannot be increased beyond 100%.
Increasing critical strike chance
Critical strike damage
Champions and units have a base 50% bonus critical damage. On average they deal 112.5% of their physical damage.
Increasing critical strike damage
Items
Reducing critical strike damage
Increasing critical strike damage
Traits
Items
Reducing critical strike damage