Shields

Version 0.28: 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 on one hand, preventing the use of two-handed weapons; they make use of 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. Some other effects can also grant you an SH score.

Shield Penalties

Wearing a shield also gives penalties to attack speed, EV, and spellcasting. While the penalty for wearing a small buckler is almost negligible, a tower shield can seriously slow your attacks and make spellcasting unreliable.

Specifically, your shield penalty is 2/5 * encumberance^2 / (20 - 3 * size_factor) * (27 - shield_skill) / 27 . This is your penalty to your evasion, which gets used to calculate everything else.

Shield type	Shield Encumberance
Buckler	5
Kite shield	10
Tower shield	15

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.

Egos

All three types of shields can spawn with the following egos:

• ~3%, resistance
• 10%, fire resistance
• 10%, cold resistance
• 10%, poison resistance
• 10%, positive energy
• 19%, reflection
• 39%, protection

Shields of cold and fire resistance can occasionally be found in ice caves and volcanoes.

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 (amulet of reflection, Qazlal's Storm Shield, or the Shining One's Divine Shield) or have the Large Bone Plates mutation. Your ability to block missiles doesn't benefit from missile-repelling effects like a scarf of repulsion, and you cannot benefit from any form of shield while you are confused.

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

• Bolt spells: Bolt of Fire (Starburst), Lightning Bolt, Bolt of Cold...
• Explosions: Fireball, Damnation, Fire Storm, Conjure Ball Lightning, Lee's Rapid Deconstruction, exploding-branded weapons
• Electrical discharges: 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:

• Ranged weapons like Bows or Slings
• Spells that fire projectiles like Iron shot, Poison Arrow, Orb of Destruction, Lehudib's Crystal Spear, Throw Icicle, Stone Arrow, Throw Flame, Throw Frost, Sting, Sandblast

If the attacker's pierce value is less than the defender's blocking value (see below for details), 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.

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)

and then on top of either of those:

+ Divine shield bonus
+ Qazlal shield bonus
+ Mutation bonus
+ Amulet of reflection bonus
+ Any SH bonus from artifacts

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

Size	Races	Buckler	Kite Shield	Tower 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 DEX * 38 * (base_shield + 13) / 26 ,

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

• Mutation bonus is +4/6/8 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.

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 0.28, shield penalty could be eliminated before 27 Shields (4 skill for buckler, 15 for kite shield, 25 for tower shield). The two larger shields used Str+Dex to determine SH, and shields had a to-hit penalty.
• In 0.27, the shield penalty increased.
• Prior to 0.25, kite shields were known as just "shields" and tower shields were called "large shields".
• 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.