Parrying

Parry is 3 + half a melee skill dropping any fractions and the weapon (or limb) must be not be unreadied.(MELEE/2)+3; round down.You can parry without a skill using DX/2+3.per B376-B377 This isn't mentioned under the Combat Lite rules, however.
Parrying is allowed with empty hands (even for people without any combat training) or with reach C weapons (such as a knife, though those had parrying penalties).Basic Set, p.392 Back in 3e, you could not defend at DX default.Classic Basic Set, p.114
You can use long weapons in close combat, but at a -4 penalty for its longest reachMartial Arts, p.117—though it may be easier to retreat or dodge. If the weapon has Reach "C, 1" you still receive the penalty, but you can still counterattack easily.
==Parrying with Adjustable Weapons==
Can you parry with a long chain weapon, such as kusari? Yes. But as it becomes unable to parry after an attack and has a -2 to parry, it may be better to dodge.
==Parrying Makes Contact==
:TG22 "A successful parry allows the defender to avoid the effects of the attack, but involves some contact."
Parrying makes contact with whatever object you're parrying with, even your hands! This can be dangerous if you're parrying unarmed against a creature that can infect on touch! This includes Infectious, Contact Disease, Infected Touch, and Pestilent Presence, etceteraZombies, p.109. Gloves or gauntlets can avoid this.
* A failed unarmed parry against a weapon means your attacker may choose to hit his original target or the arm you parried withBasic Set, p.376-377
* A successful destructive parry attacks the your attacker's shield on a block, weapon on an armed parry, or arm on a bare-handed parryPowers, p.165
* A successful aggressive parry technique may target your attackers weapon, limb or hand (see page)Martial Arts, p.65
This is a custom rule for the technique though, much like how retreats are forbidden.
==Parrying Without Contact==
*The Power Parry in GURPS Powers does not create contact since they are using a power instead of a limb.
*Using Telekinesis to parry also does not involve contact with the user, since they are using the invisible set of hands to do the parrying.
MA122's "What Is . . . a Parry?" box (2nd paragraph) introduces a new "Not every parry involves contact" policy under a new yanking option which ignores Parrying Heavy Weapons:
:"A parry against an attack on your weapon or your hand represents yanking the target out of harm’s way"
==No-Hand Parries==
Basic Set see One Hand which allows unpenalized parries using a limb instead of a hand.
It's unclear whether or not this is allowed for creatures who have hands. Perhaps it might be reasonable to allow it but at a -1 penalty (-2 skill "doing two things at once") for keeping the hand/wrist out of the way.
Exploits 49:
:Monster Parries: Natural beings without hands (like most animals) can’t parry; they can only dodge. Monsters aren’t natural! Many can parry – sometimes using body parts that count as weapons, not bare hands.
==Parrying with Improvised Weapons==
3eB99:
:You can also parry with a non-weapon of the proper size and shape, using the closest weapon skill.
:A pole or rifle could parry like a spear, a bow like a light club.
:However, parrying just once with a bow will ruin it as a bow. though it may survive for a few seconds longer as a club.
There is a cinematic advantage that gives bows DRs for parrying in one of the Dungeon Fantasy books.
==Parrying Firearms (Equilibrium style)==
===Parrying Firearms in Close Combat===
Kromm in 2010 http://forums.sjgames.com/showpost.php?p=1031996&postcount=5
:A pistol (or any other firearm) used in close combat is considered a melee weapon, which is why you can parry it (p. B376)
===Parrying other Missile Weapons===
B327
:If a foe attacks you with a missile weapon and he is within reach of your melee weapon, you may parry.
:Success would mean that you slapped his bow or gun aside, causing him to fire wide of your body.
B376 says:
:If a foe attacks you with a missile weapon and he is within reach of your melee weapon, you may parry.
:You’re parrying the weapon, not the projectile!
:For example, if an attacker fired a pistol at you from only one yard away, you could attempt to parry barehanded.
:Success would mean that you slapped his arm or gun aside, causing him to fire wide of your body.
"from only one yard" (maximum 1 yard) actually refers to sharing the same hex, and not being an adjacent hex, as Kromm's quote above indicates.
*This may be because punches are reach C weapons, and because a pistol occupies the hex of the shooter and not any adjacent hexes. See next section for more about this.
One critical semantic difference above is B376 refers to slapping the ARM while B327 does not. The critical observation here is that "he" is in range of the weapon, so his ARM also is.
===Distinction===
In respect to wanting to parry a weapon instead of the arm wielding it, it should not matter if the "foe" is in reach, only that the weapon is.
This distinction matters as long weapons can occupy hexes in front of their wielders without the wielder being targetable in thoses hexes. B400's Striking at Weapons has a chart showing that, explained in B401's Striking at Weapons in Tactical Combat.
TS25 says any firearms besides pistols have reach C,1.
==Parrying Firearms==
*There is a penalty to parrying a firearm if it's being fired from the hip.Tactical Shooting, p.11
* Long guns occupy a hex in front of the shooterTactical Shooting, p.25
Logically this should only help if the parrying is the one being aimed at, so the shooter has turned to face him so that the firearm is occupying a hex within their reach.
GURPS Tactical Shooting p.25 under Close-Contact Shots
:If your gun can touch your victim, you’ll rarely miss.
:At Reach C with a weapon used with Guns (Pistol),
:or Reach C or 1 with any other firearm, All-Out Attack (Determined) gives +4 to hit, as with a melee attack, instead of +1.
:However, your target may attempt a melee parry against such an attack (p. B376).
Some might read "such an attack" as only when using AOA:Determined. When viewed in combination with B327/B376 however, it could be viewed as referring to and amending the rules for parrying ANY attack from that range (including normal ones) allowing reach-1 parries against rifles.
===Combined Consideration===
A normal person with reach C hands (as of 4e) can parry a rifle (reach 1) aimed at them from someone in an adjacent hex. This is at least true in the case of AOA:Determined, even if disputes might arise as to whether or not this applies to non-All-Out attacks.
A "giant" person (SM+1) improves his reach C to reach 1. This allows him to parry PISTOLS wielded by foes in adjacent hexes...
It stands to reason that in cases where both of these apply (a reach 1 person parrying a rifle) that this ought to be possible at TWO hexes away.
Furthermore, where a bayonet gives a rifle a stabbing reach of 2 (meaning it occupies TWO hexes ahead of the rifle-wielder) a reach-C parry should be able to parry it from two hexes away and a reach-1 parry should be able to parry it from THREE hexes away.
A pair of reach 2 bayoneters should be able to parry from FOUR hexes away. Basically the tips need to be sharing a hex. This isn't spelled out but it's a logical extension.
==Size Modifier==
Gigantism per Size Modifier and Reach increases the reach of punches from C to 1 in 4e.
==Steps==
Martial Arts introduced the idea of a slip which allowed moving 1 step towards a foe as part of an active defense.
It's unclear whether or not this would allow parrying a firearm from an increased range.
==Lunging==
Normally getting +1 reach to a punch in 4e requires using a maneuver like All-Out Attack (Long) and Technical Grappling introduced Committed Attack (Long) for grapples (though it could be adapted to strikes by penalizing damage instead of control points)
Great Lunge is a form of extra effort normally used on attacks to get a similar effect without limiting maneuver selection. However if a GM were to allow this to be used on an Active Defence (this would be a house rule) it might represent an alternative (or supplement) to a "slip" to get extra reach for parrying firearms at greater distances.
==Quotes==
===Kromm in 2006===
http://forums.sjgames.com/showpost.php?p=302932&postcount=2
In GURPS, "parry" does not only mean "stop cold," or what most unarmed fighters call a "block." It can also mean any slight deflection good enough to let you evade an attack with a partial step smaller than a hex on a battle map. A matador with a cape "parries" a bull. He doesn't stop the horns with his cape . . . he uses his cape to guide the bull past as he turns. That's what most parries are in GURPS. Hard meet-force-with-force parries aren't normally assumed. This is why even though weapons can break on any parry in real life, we only make that possible in the game when there's a factor-of-three weight difference.
===Kromm in 2008===
http://forums.sjgames.com/showthread.php?p=563199#post563199
you get one additional block or parry per hand, regardless of number of hands or number of attacks
===PK in 2009===
http://forums.sjgames.com/showthread.php?t=64987
"one of the benefits of Extra Arms" in response to:
:Karate and Judo state that you can parry once with each hand, and that the cumulative penalties for parrying (-4 or -2 with TBAM) more than once accrue separately for each hand.
:If a character takes Extra Arms, is he able to parry in this manner with each of the extra hands?
Mirroring Kromm's statement the previous year
=== Kromm in 2015 ===
http://forums.sjgames.com/showpost.php?p=1962292&postcount=7 Kromm in house ruling them as deflections.
note that One Hand specifies:
:you may make unarmed parries with a handless arm, and possibly strap something to it
===Kromm in 2018===
http://forums.sjgames.com/showpost.php?p=2211561&postcount=13
*Reach: 0 for Reach C; +1 for Reach 1; +2 for Reach 2; and +3 for Reach 3+. [More surface area means it's easier to intercept a blow.]
*Balance: -1 if the weapon is unbalanced ("U" on its current Parry stat); 0 if balanced (no "U"). [Better balance means faster response to attacks.]
*Hand-Guard: -1 if the weapon lacks one; 0 if it has one of any style (basket, cross, tsuba, whatever). [Hand protection means close calls count as saves.]
*Surface: -1 if limited (blows must be received on a strong point, on or near the hilt, on or near the head, or whatever); 0 if unlimited (blows can be received anywhere on the weapon except where the hands are). [Using more of the surface area gives more options to defend.]
*Support: 0 if one-handed; +1 if two-handed. [A solidly grasped weapon is harder to push aside. This is 0/+1 instead of -1/0 because it's intended to balance against weapon-and-shield, where shields give a bonus.]
**emphasis: Support is a straightforward "two hands are stronger than one" thing. If we say adding a hand to a one-handed weapon gives +1 to Parry (and we do, in GURPS Martial Arts), then it should work that way in general. 
*Flexibility: -1 if non-rigid; 0 if rigid. [A rigid weapon is harder to push aside.]
==See also==
*Defending
*Brute Parry
*Enhanced Parry
*Hands-Free Parry
*only on parries
*Strength as Mass