Shields, Bucklers, and Parrying

Earlier this season, I'd posted a houserule regarding Dual Wielding, or Fighting with Two Weapons. Some peripheral discussion outside the post resulting from its mathematic justification lent to speculation on how to make shields simply better than dual wielding: the difference between fighting with two weapons and fighting with a two-handed weapon was very evident, but the difference between parrying with two weapons and with using a shield was less so. So I did some more math and came up with this rule, changing up shields and introducing the buckler:

Shields & Bucklers

Shields grant a flat bonus of +2 to Armor Class. Shields are strapped to one arm and consume its full use.

Bucklers, smaller metal round shields, are available for purchase. Bucklers may be worn on one arm or carried in one hand.

• If carried, the buckler takes up the full use of the arm - as a shield - but can be used as a 1d3 weapon with the Fighting with Two Weapons house rule.
  
• If strapped, the buckler cannot be used when Fighting with Two Weapons, but also does not take up the full use of the arm. Thus, a character using a buckler could also be holding a torch, or wielding a two handed weapon, including ranged weapons.
  
• In either case - carried or strapped - a buckler, on a round where the wearer does not make an attack, ranged or otherwise, grants a flat +1 AC, both to melee and ranged attacks made against the user from a direction that a shield would be applicable - making the assumption that the user is fighting defensively.
  

If using Shields Shall Be Sundered optionally, a buckler should not be able to be sundered. A generous referee might allow a sunder, but only negate half of the damage that would be inflicted by the hit - lest bucklers eclipse two weapon fighting in effectiveness.

The rule above is based on the historical use of bucklers as companion weapons, with an eye towards synergy with preceding house rules.

How Does This Affect Combat?

As already established in the dual-weapons article, the value of a single point of Armor Class, using the Fighting Man THAC0 tiers, is - based on the weapon being used - as follows:

	d4	d6	d8	d10
Dmg. Delta:	-0.125	-0.175	-0.225	-0.275

This is consistent across the board: so, if wearing chainmail and being attacked by a monster of - say - 2 hit dice (THAC0 17) with an attack dealing 1d8 damage, a hero can expect to take 2.025 damage per round until the enemy can be eliminated (see appended chart at the end of the post).

• The hero, if fighting defensively with two weapons or fighting defensively with a buckler, would expect to take 1.8 damage per round instead.
• If the hero was using a buckler and made no attacks during the round, they would expect to likewise take 1.8 damage per round instead: including against - say - a 2 HD archer with a 1d8 ranged attack.
• The hero, if fighting with a buckler and a two-handed sword, would be able to to opt in to 1.8 damage per round, as well, by not making an attack - but would expect to take 2.025 again if they press the attack.
  
• A character using a shield, regardless of their stance, would expect to take 1.575 damage per round.
  

This would at first glance imply that - over short engagements - there is little advantage to be had. Over 10 rounds fighting defensively in melee, a character with a buckler would expect to take barely 3 points of damage more than if they used a shield. However - consider that most combat-focused characters aren't going to be hit every round - especially if coupling the shield with plate armor. Instead, most low level enemies have a better chance of missing than they do of hitting - our hero from above will likely not be hit for three or four combat rounds before being hit for 4 or 5 in one strike! In a game where protracted combats work against the good of the party - hit points being one resource to manage: a resource that is in ever-short supply - being able to forestall the likelihood of being hit even one more round while the damage dealers are able to knock out enough monsters to shake their morale may be the difference between spending those precious hit points and preserving them. Based on the the likelihood to be hit at a given Armor Class, the number of rounds a character can expect to go per hit taken breaks down as follows:

	Armor Class
THAC0	9	8	7	6	5	4	3	2
19	1.82	2.00	2.22	2.50	2.86	3.33	4.00	5.00
17	1.54	1.67	1.82	2.00	2.22	2.50	2.86	3.33
14	1.25	1.33	1.43	1.54	1.67	1.82	2.00	2.22
12	1.11	1.18	1.25	1.33	1.43	1.54	1.67	1.82
10	1.05	1.05	1.11	1.18	1.25	1.33	1.43	1.54

Versus a 2 HD monster, a character with chainmail only will, on average, expect to be hit no fewer than once every three rounds of combat in which they are participating. With a buckler fighting defensively, this increases to just over every third round; with a shield, the same character is likely to be hit every fourth round. Of course, this is per monster - so, fighting against three or four monsters increases the odds, but knowing the above - would your party prefer 2 chances to kill the enemy before it wounds your Fighting Man at AC 5 or would your party prefer 4 chances at AC 3?

For completeness, as follows is a table containing the % chance of scoring a hit at each level tier and the damage per round that will be inflicted by a competing Fighting Man - bonuses from high Strength or magic weaponry excluded - of a given level using a given damage die.

Delve on, readers!

Expected Damage and Hit Likelihood; by Tier, AC, and Damage Die

		Armor Class
Ftr. Tier	THAC0	9	8	7	6	5	4	3	2	1	0
		Chance to Hit
1-3	19	55%	50%	45%	40%	35%	30%	25%	20%	15%	10%
4-6	17	65%	60%	55%	50%	45%	40%	35%	30%	25%	20%
7-9	14	80%	75%	70%	65%	60%	55%	50%	45%	40%	35%
10-12	12	90%	85%	80%	75%	70%	65%	60%	55%	50%	45%
13-15	10	95%	95%	90%	85%	80%	75%	70%	65%	60%	55%
		Rounds Passing per Expected Hit
1-3	19	1.82	2.00	2.22	2.50	2.86	3.33	4.00	5.00	6.67	10.00
4-6	17	1.54	1.67	1.82	2.00	2.22	2.50	2.86	3.33	4.00	5.00
7-9	14	1.25	1.33	1.43	1.54	1.67	1.82	2.00	2.22	2.50	2.86
10-12	12	1.11	1.18	1.25	1.33	1.43	1.54	1.67	1.82	2.00	2.22
13-15	10	1.05	1.05	1.11	1.18	1.25	1.33	1.43	1.54	1.67	1.82
		Damage per Round, D4
1-3	19	1.375	1.25	1.125	1	0.875	0.75	0.625	0.5	0.375	0.25
4-6	17	1.625	1.5	1.375	1.25	1.125	1	0.875	0.75	0.625	0.5
7-9	14	2	1.875	1.75	1.625	1.5	1.375	1.25	1.125	1	0.875
10-12	12	2.25	2.125	2	1.875	1.75	1.625	1.5	1.375	1.25	1.125
13-15	10	2.375	2.375	2.25	2.125	2	1.875	1.75	1.625	1.5	1.375
		Damage per Round, D6
1-3	19	1.925	1.75	1.575	1.4	1.225	1.05	0.875	0.7	0.525	0.35
4-6	17	2.275	2.1	1.925	1.75	1.575	1.4	1.225	1.05	0.875	0.7
7-9	14	2.8	2.625	2.45	2.275	2.1	1.925	1.75	1.575	1.4	1.225
10-12	12	3.15	2.975	2.8	2.625	2.45	2.275	2.1	1.925	1.75	1.575
13-15	10	3.325	3.325	3.15	2.975	2.8	2.625	2.45	2.275	2.1	1.925
		Damage per Round, D8
1-3	19	2.475	2.25	2.025	1.8	1.575	1.35	1.125	0.9	0.675	0.45
4-6	17	2.925	2.7	2.475	2.25	2.025	1.8	1.575	1.35	1.125	0.9
7-9	14	3.6	3.375	3.15	2.925	2.7	2.475	2.25	2.025	1.8	1.575
10-12	12	4.05	3.825	3.6	3.375	3.15	2.925	2.7	2.475	2.25	2.025
13-15	10	4.275	4.275	4.05	3.825	3.6	3.375	3.15	2.925	2.7	2.475
		Damage per Round, D10
1-3	19	3.025	2.75	2.475	2.2	1.925	1.65	1.375	1.1	0.825	0.55
4-6	17	3.575	3.3	3.025	2.75	2.475	2.2	1.925	1.65	1.375	1.1
7-9	14	4.4	4.125	3.85	3.575	3.3	3.025	2.75	2.475	2.2	1.925
10-12	12	4.95	4.675	4.4	4.125	3.85	3.575	3.3	3.025	2.75	2.475
13-15	10	5.225	5.225	4.95	4.675	4.4	4.125	3.85	3.575	3.3	3.025

Public domain art lovingly pilfered from OldBookIllustrations.com and adapted for thematic use. Attribution in alt text.