Critical Hits
Critical hits multiply the damage of a successful physical attack or damaging jutsu before the target's reductions are applied.
For a normal shinobi, critical chance starts at 5%. The Precision skill increases it on a diminishing-return curve, up to the combat hard cap of 35%. Some nature/build bonuses can contribute as well, but the final chance cannot exceed that cap in the standard calculation.
The standard critical multiplier is 1.5×. Because defense, shields, PvP protection and boss soft caps are applied afterward, a critical does not always show exactly 50% more HP loss on screen than a nearby non-critical hit.
Precision therefore does two useful things with the current combat rules: it raises your critical chance and makes an opponent's manual Dodge less reliable. /state shows your effective combat values if you want to compare builds.