Defense Rating

Defense does one thing: it is the DEF in the Chance to Hit formula, so it lowers how often a weapon attack lands on you. It never lowers the damage of a hit that does land, and spells and elemental skills never check it. That is why 20,000 defense on a sorceress is nearly worthless against Hell's casters, and why it matters against Hell's melee packs.

The order

The Amazon Basin's order for building the defender's number, which the game applies for every attack rolled:

1. Armour — the base armour's own defense (armor.txt minac–maxac).
2. Ethereal bonus on an ethereal piece.
3. [[enhanced-defense]] on the piece itself.
4. [[defense]]: flat "+X Defense" and the Dexterity contribution (a quarter of a point per Dexterity).
5. Minus Monster Defense Per Hit (on monsters).
6. The Stone Skin unique monster bonus.
7. Inner Sight (the Amazon's aura on the target).
8. "% Defense": the percentage from skills such as Shout and Defiance.
9. The Berserk penalty (Berserk sets the Barbarian's defense to 0 for its duration).
10. Defense vs. Melee and Defense vs. Missile, against the attack's kind.
11. Target Defense Reduction: "−X% Target Defense" on the attacker's weapon.
12. Ignore Target's Defense: sets the number to 0 against the monsters it works on.

chance to be hit = 100 × 2 × AR ÷ (AR + DEF) × alvl ÷ (alvl + dlvl), held between 5% and 95%

Doubling defense never halves the hits taken: the first half of the formula is AR ÷ (AR + DEF), so each doubling removes less than the one before, and the 5% floor is always there.

Running

The Basin's rule, in its words: "when a player character is running, hit checks are not made for any attacks made while doing so and these attacks always hit", with Leap, Leap Attack, Whirlwind and Charge as the exceptions that still roll. Walking keeps the roll — and keeps Blocking at its full value instead of a third.

Where it ends

A hit that lands goes to Taking Damage: Energy Shield, flat reduction, Physical Damage Reduction and absorb decide what it costs. Defense has no say past the roll.