Knockback

Knockback is a mechanic that determines if a subject is moved or launched from an attack.Basic Set, p.378 It is primarily caused by Crushing damage, and Cutting damage that fails to penetrate Damage Resistance. When shoving an inanimate object, you may use its HP to roughly gauge its mass -- or just use Lifting and Moving Things instead (12xBL).
== Sumos and Stringbeans ==
Character's physical builds can affect their resistance to knockback. The Skinny disadvantage gives an effective -2 to resisting knockback, while Overweight, Fat, and Very Fat give +1, +2, and +3 respectively.Basic Set, p.18-19String Beans should be two words but it doesn't read as well as "Stringbeans".
== Realistic ==
=== By Rules as Written ===
Knockback depends on basic damage rolled before subtracting DR. For every full multiple of the target's ST-2, move the target 1 yard. A subject knocked back this way must attempt a DX, Acrobatics, or Judo roll, -1 per yard moved.
Knockback is nearly unused in realistic or gritty campaigns, as any crushing attack that's strong enough to push a body backwards (i.e. an explosion doing a multiple of the subject's own ST) is also guaranteed to also put the target into negative HP. The one exception to this is a shove,Basic Set, p.372 which does no damage but double knockback, which may do just enough knockback to force an opponent off a cliff or into some dangerous obstacle.
==== Example ====
Arthur Green (ST 12) is wearing an TL8 assault vest with trauma plates (DR 28 for the torso). Zach Red (ST 12) ambushes him, hitting him with a baseball bat (sw+1 crushing) in an all-out attack (1d+5 cr). On a lucky hit, Zach rolls 11 damage -- just enough to pass Arthur's minimum knockback damage of 10 (ST 12 - 2). Zach's attack does 0 damage, but pushes Arthur Green back a single yard, which is just enough to make Arthur roll for Judo to avoid falling over. Arthur rolls a 14 vs his Judo of 12 and gets knocked down.
== Cinematic ==
=== Homebrew: Barbarian Launches ===
For more of a cinematic feel for shoves, throws, and launches, use: (Fighter's ST - Victim's ST) to determine Yards of distance. Bonuses from Sumo Wrestling give a flat bonus to effective ST, as does Lifting ST. As per Powers, you can toss an enemy half as far upward. If disarming an enemy (with bare hands, whip, jitte, etc.), you may launch an enemy's weapon just as far -- choose a direction that's inconvenient for them! 
Launching enemies does Yards crushing damage upon a launch (as crushing) and another Yards damage if the target collides with something (like fall damage). Knockback has a Yards penalty to DX, Acrobatics or Judo to stay upright. If colliding with a wall or other immobile object, the thrown subject can remain upright, but uses Acrobatics, Judo, or even Breakfall to reduce their damage. Catfall can help, and creatures with natural "air brakes" or wings can reduce their damage as if falling.
Furthermore, treat any bonus to crushing damage from a weapon (such as from a mace, club, maul, etc.) as a bonus to ST for the purposes of launching. Any successful hit does its normal damage plus launching. Any creature knocked unconscious by the hit (around 0 HP) doesn't roll to reduce fall damage, and may even knock into other enemies!
==== Examples ====
Arthur Green (ST 12) is wearing an TL8 assault vest with trauma plates (DR 28 for the torso). Zach Red (ST 12) ambushes him, hitting him with a baseball bat (ST+3 for launches) in an all-out attack (+2 ST). Zach is striking at an effective ST 17, five points over Arthurs'. Zach's attack does 0 damage (blocked by Arthur's armor), but knocks Arthur Green a full five yards down the alley, crashing him into a pile of trashcans. Zach rolls a 14 vs a 7, failing a chance at a graceful landing, and takes five points of injury from falling into the cans.
=== Homebrew: Resistance by HP ===
Use the average of ST and HP for determining resistance to throws. This lets meaty characters (who are already defending the front line) avoid being knocked back. As such:(ST + HP) / 2Note that this is for living creatures -- an Unliving zombie can easily have 20 HP from its general toughness, but not be any more massive than a human of the same size.
==Powers==
GURPS Powers:
*137 - knockback is vertical (no % modifiers listed)
*165 Coordinated Attacks can create knockback with multiple attackers which could not be accomplished independently for either
*166 - halve “knockback” for a vertical launch
**Success lets him add his broad-jump distance to horizontal knockback, his high-jump distance to vertical knockback.
==Martial Arts==
===Bracing===
GURPS Martial Arts 52 has Brace from Teamwork to resist it better. There doesn't seem to be any problems with potentially squishing someone. For example a ST 100 dragon using Brace against a mouse who is shoved by another dragon. Even if you could prevent the knockback, that should cause some damage!
One solution might be applying Blunt Trauma to shoving attacks, so they could potentially be injurious. Treat the non-damaging aspect of shoves as if it were an attack stopped by DR!
For fairness, apply BT as bonus damage to all strikes regardless of whether or not they hit DR. This helps with weirdness of BT potentially doing more damage than damage which exceeds DR by 1, and also makes physical attacks more competitive, which is useful if using house rules like Shrug It Off
This is an oversight similar to how the interaction of KB and Grappling is not looked into (like for example, what happens it 2 teammates link arms and 1 gets shoved, if their grapple could be compromised by that or not, if both get knocked back, etc)
===Defense or Resistance===
107 clarifies:
:The GM should consider extending the -2 for “trying to do two things at once” to all success rolls except defense and resistance rolls against enemy attacks. For instance, it would modify DX rolls to evade or to keep someone from .. rolls to stay standing after suffering knockback
This clarifies that the DX roll to avoid falling, even though it happens in response to an attack, is not actually a defense or resistance roll.
===Push Kick===
This alternative shove using the leg was introduced on MA78
==Technical Grappling==
GURPS Martial Arts: Technical Grappling on page 12's Armed Grappling under Seizing a Weapon or Object talks about seized objects being considered part of the hands grappling the object. This could be useful in considering collective mass being knocked back less.
==Quotes==
===Kromm===
2014 http://forums.sjgames.com/showpost.php?p=1713589&postcount=9
: I'd urge a reading of Dealing with Charging Foes (GURPS Martial Arts, p. 106). "Stop thrust" is simply an old fencing term . . . the name comes not from checking the foe's advance but from checking his attack. A stop thrust truly stops the foe only if the injury kills him, renders him unconscious, or leads to knockdown and stun; it slows him down only if it causes knockback, was aimed at and cripples a leg or a foot, or reduces him below 1/3 of his total HP. The rules in Martial Arts present an additional option wherein a successful stop thrust may impose movement limitations even if the injury isn't especially severe.
Feb 2018 http://forums.sjgames.com/showpost.php?p=2154884&postcount=31
:If you hit a foe hard enough to cause knockback, that foe will need extra movement to get to you. If they have insufficient movement left for that (they took a maneuver that allows only a step and thus cannot step again, or they could just barely get to you and now they're a hex or two short), too bad for them.
===PK===
2007 http://forums.sjgames.com/showpost.php?p=436412&postcount=10
In this Pyramid article I priced Knockback as a Common threat, with resistance adding to effective ST. It just makes sense. (Note that immunity is a mere 15 points, not 30.)
==See also==
*Double Knockback
*No Knockback
*Recoil Rocket
*Shove
Category:Rules