Shields

Version 0.19: This article may not be up to date for the latest stable release of Crawl.

“Let who will boast their courage in the field, I find but little safety from my shield. Nature's, not honour's, law we must obey: This made me cast my useless shield away, And by a prudent flight and cunning save A life, which valour could not, from the grave. A better buckler I can soon regain; But who can get another life again?” -Archilochos. 7th cent. B.C. trans. William H. Goodwin, 1878.

Shields are a kind of armour worn in one hand, preventing the use of two handed weapons, which use the Shields skill. Unlike other armour, shields increase a character's SH defense, giving you a chance at blocking physical (and some magical) attacks entirely. Certain spells can also grant you an SH score.

Shield Penalties

Wearing a shield also gives penalties to attack speed, attack damage, and spellcasting, along with EV penalties of -0.8 (buckler), -3 (shield), or -5 (large shield). While the penalty for wearing a small buckler is almost negligible, a large shield can seriously slow your attacks and make spellcasting unreliable. Sufficient Shields skill will reduce or even negate these penalties. The amount needed varies by race, but can be found in the description of the shield in-game:

Size	Races	Buckler	Shield	Large shield
Little	Spriggan	7.2	-	-
Small	Kobold, Halfling	5.6	21	-
Normal	most races	4	15	25
Large (normal torso) & Formicids	Centaur, Naga, Formicid	2.4	9	15
Large	Ogre, Troll	-	9	15

Your Shield penalty is (Shield EV penalty) - (Shields skill)/(5 + (Size factor)). Shield EV penalty and Size factor can be looked up in these tables:

Shield type	Shield EV penalty
Buckler	-0.8
Shield	-3
Large shield	-5

Size	Races	Size factor
Little	Spriggan	+4
Small	Kobold, Halfling	+2
Normal	most races	0
Large (normal torso) & Formicids	Centaur, Naga, Formicid	-2
Large	Ogre, Troll	-2

When attacking with any kind of weapon (including unarmed), if you are wearing a shield and your Shield penalty is greater than zero, the game throws two dice with (Shield penalty) sides. The smaller value rolled is added to your attack delay.

Blocking

Effect

It's possible to block a melee attack or a ranged projectile attack if you wear a shield of some kind or are under the effect of a magical shield (the Helm card's Magic Shield, Qazlal's Storm Shield, or the Shining One's Divine Shield) or have the Large Bones Plates mutation. Your ability to block missiles doesn't benefit from spells like Repel Missiles or Deflect Missiles. If the attacker's pierce value is less than the defender's blocking value, the attack does no damage. Shield blocking is done before rolling your evasion or your AC, but if you have already blocked some attacks in that turn, your blocking ability will be decreased greatly. You cannot benefit from a shield you are wearing while you are confused, but shields from other sources will still protect you.

All melee attacks can be blocked (except a successful stabbing), but many ranged attacks are unblockable:

• Bolt spells: Bolt of Fire, Bolt of Cold, Lightning Bolt, Bolt of Draining, Venom Bolt, Bolt of Magma, Bolt of Inaccuracy, Shock, and the 4th ray of Searing Ray
• Explosions: Fireball, Hellfire, Fire Storm, Conjure Ball Lightning, Lee's Rapid Deconstruction, exploding-branded weapons
• Other electricity-based beams: Static Discharge, Chain Lightning
• Enchantments: Agony, Pain, Confuse, Mesmerise, etc
• Beams with perfect accuracy: Magic Dart, Sticky Flame (only the player's version)
• Other ranged attacks that are not beams: Shatter, Tornado, Airstrike, Smite, Ozocubu's Refrigeration, Freeze, etc
• Penetration-branded weapons (primarily javelins)

Some examples of ranged attacks that can be blocked: Iron shot, Poison Arrow, Orb of Destruction, Lehudib's Crystal Spear, Iskenderun's Mystic Blast (the explosion is special), Throw Icicle, Stone Arrow, Throw Flame, Throw Frost, Flame Tongue, Sting, Sandblast

Calculation

The defender's blocking value depends on the nature of the shield:

Physical shields:

SH = Block × (1 + Shield skill/40)
+ Enchantment bonus + Stat bonus 
+ min(0.38×Shield skill, .57 + 0.19×Shield skill)

or Helm card (this does not stack with a physical shield):

SH = 4.5 + 0.375×Invocations

and then on top of either of those:

+ Divine shield bonus
+ Qazlal shield bonus
+ Mutation bonus
+ Cigotuvi's Embrace bonus
+ Amulet of reflection bonus
+ Any SH bonus from artifacts
 

For a physical shield (Buckler, Shield and Large Shield), Block is the shield's blocking value, equal to the base shield bonus (3 for Buckler, 8 for Shield, 13 for Large Shield), modified by a size factor:

Size	Races	Buckler	Shield	Large shield
Little	Spriggan	+2	-	-
Small	Kobold, Halfling	+1	+0.5	-
Normal	most races	0	0	0
Large (normal torso) & Formicids	Centaur, Naga, Formicid	0	0	0
Large	Ogre, Troll	-	-0.5	0

• Stat bonus is 38×DEX for bucklers, 19×STR + 19×DEX for shields, or 26×STR + 12×DEX for large shields. Then this value is multiplied by (block + 13)/26, and by 100.

• The Shining One's Divine shield bonus is based on Invocations skill.

• Mutation bonus is +2/4/6 SH depending on your level of the Large Bones Plates mutation.

The resulting value is rounded to the nearest integer and displayed as the player's SH value.

For reference, a 15-Dex, 15-Str character wearing a buckler has an average blocking value of:

• 3 with a Shield Skill of 0
• 6 with a Shield Skill of 8
• 8 with a Shield skill of 15
• 11 with a Shield skill of 27

With a large shield, it becomes:

• 11 with a Shield Skill of 0
• 15 with a Shield Skill of 8
• 19 with a Shield skill of 15
• 25 with a Shield skill of 27

The attacker's pierce value is equal to:

1d(15 + to hit/2 + 5×past_blocks^2) - 1 (melee attacks)

1d(1.3×to hit    + 5×past_blocks^2) - 1 (ranged attacks)   

"To hit" is the monster's To hit value (based primarily on the monster's HD, type, and weapon accuracy) and "past_blocks" is the number of attacks already successfully blocked in the current turn.

The defender's blocking value is equal to:

 2d(2×SH)/6 - 1.3 (Divided by 3 against melee attacks from invisible opponents)

If this value is greater or equal than the attacker's pierce value, the attack is blocked.

History

• Prior to 0.17, unarmed attacks had a speed penalty when attacking with a shield equipped.
• Prior to 0.16, the amount of skill required to negate penalties for wearing a shield were more complex.