Knockback is the measure of how far an attack sends its target. For most attacks, knockback increases as damage on a character increases. An example of an attack with high knockback is Bowser's forward smash; it launches opponents very far, so far that at high damages it's more powerful than a Home-Run Bat's smash attack. Pikachu's neutral attack, on the other hand, has very low knockback - it hardly sends opponents anywhere, even at ludicrous damages. Attacks with relatively low knockback tend to be good for combos.
The knockback of almost every attack works in tandem with the target's damage - it increases as the target's damage gets higher. It is also affected by the target's weight, gravity, and a few other conditions (such as type effectiveness). While not the primary factor, the damage dealt by an attack is a significant factor in how much knockback it deals - this is the reason stale moves have less knockback than fresh ones, and the reason smash attacks deal significantly more knockback when fully charged.
Each hitbox of a move has two knockback values: a base knockback and a knockback scaling (also known as knockback growth). Base knockback is the minimum amount of knockback the attack can deliver under normal circumstances, and knockback scaling is a factor that controls how much the knockback increases as damage increases.
Moves with high base knockback can deal high knockback (such as performing a forward smash with the Home-Run Bat), even against fighters who haven't taken much damage, and tend to be more effective at KOing when fighters can easily be sent flying at low damage percentages (such as against lighter fighters, when near the edge of the stage, or when a fighter is handicapped to sustain more knockback). Tiny-sized fighters are usually the most vulnerable to getting KO'd by high base knockback attacks, due to having reduced weight, and an increased knockback taken multiplier.
On the other hand, moves with high knockback scaling can reach KO potential more quickly (such as Luigi's forward smash), especially if they have a high damage output, and tend to be more effective at KOing when fighters need to take greater knockback than what a high base knockback attack can deliver on its own (such as against heavier fighters, when far away from a stage's blast line, or when a fighter is handicapped to sustain less knockback). Advanced techniques to extend survival, such as DI and momentum canceling, are also less effective the stronger a move's knockback scaling is.
In Melee, the highest knockback delivered and received by each character is given in a match's results screen, labeled as "Fastest Pitch" and "Top Speed" respectively, though the numbers lack meaning. In Brawl, the velocity applied (in units per 1000 frames) is provided instead of the knockback value (though it's simply knockback divided by 0.03). The unit is given as "mph"; while this would presumably mean "miles per hour", this is obviously not the case, as a 1,000 mph hit would barely send characters anywhere. In Super Smash Bros. for Nintendo 3DS, knockback units are again shown without a meaning, while in Super Smash Bros. for Wii U, they are measured in "mph" as in Brawl, though in a lower scale. Strangely enough, knockback for a same move between the two games is actually shown in different scales: Ganondorf's Warlock Punch, for instance, scores 102 units of knockback against Mario at 0% damage (without other modifiers) in Smash 3DS, while scoring 53 mph under the same conditions in Smash U. Despite these differences among games, they all internally use the same knockback measurement units in accordance to the knockback formula, as evidenced by moves with unchanged damage and knockback values throughout them (such as Jigglypuff's back throw from Melee to Smash 4) keeping their knockback identical.
The following table gives an idea of various knockback strengths:
In Super Smash Bros. Ultimate, when hitstun exceeds 32 frames, the process of the character getting launched is sped up for a duration proportional to the hitstun inflicted. This is especially noticeable near KO percentages, where characters fly away very quickly, then come to a stop almost immediately, effectively causing the launch to execute much faster. The effect is also more noticeable for moves which have high hitstun modifiers, such as Isabelle's neutral attack, which can even trigger the effect before the knockback is strong enough to cause tumbling. Because of this change, the hitstun they experience scales much more slowly at higher knockback values. According to director Masahiro Sakurai, this change was implemented to increase the overall speed of the game, by reducing the time during which launched characters are incapacitated. The visual and mechanical differences this effect causes on knockback are notorious enough that it is often dubbed "balloon knockback" by the community, as it has similar physics to hitting a balloon in real life. Moves with set knockback retain traditional knockback physics.
Launch rate, also known as Damage % in Super Smash Bros. and Damage Ratio in Melee and Brawl, is a feature in all Super Smash Bros. games that alters how much knockback is given and received (despite its name in Melee and Brawl, damage is unaffected).
All knockback in a match is multiplied by the launch rate value, which by default is 1.0×. This value can be set from as low as 0.5× (attacks have half knockback) to as high as 2.0× (attacks have double knockback). The minimum launch rate is ideal for combos, while the maximum launch rate is ideal for KOing opponents at extremely low percentages. However, the latter also affected attacks with set knockback up until Smash 4 and Ultimate, causing multihit attacks to not always combo into each other.
In competitive play, nonstandard launch rates are difficult to detect during games, which has led to some tournament matches unintentionally having been played at an incorrect launch rate. A notable example of this was a set between Armada and SilentSpectre at Pound 4 in 2010 that was played at 0.9×; this remained undiscovered for nine years. The infamous matches between komorikiri and CaptainZack, and ZeRo and Dabuz at GENESIS 4 are more recent examples. Both matches were being played at a launch rate setting of 0.9×. The latter match gained notoriety, and soon became an inside joke in the community.
There has been some discussion among Brawl's competitive community as to whether using a launch rate value other than the default 1.0 results in a more healthy metagame; 1.1× is a commonly-mentioned value claimed to make many polarizing attack chains (such as using Sheik's forward tilt into itself endlessly) less viable while also shortening the length of stocks. The idea has never attained serious consideration among tournament organizers.
Appearing in all games to date, visual effects known as angle indicators show when a hitbox collides with an opponent; as its name suggests, the angle indicator shows the angle of said hitboxes. In Brawl, angle indicators show different colors depending on who or what they hit. For player one, the angle indicator is red, with the second player's indicator being blue, and so forth. Computer-controlled opponents and objects like Sandbag have white angle indicators. Angle indicators appear in Super Smash Bros. as small "bubbles" appearing in the direction of the angle. In Smash 4, angle indicators appear as colorful, stylized "debris" flying off of an impact.
Smoke trails also indicate the angle at which a character is knocked away, but only appear when a character has taken a lot of damage, and are thus much less useful. In Smash 4, said smoke trails at higher knockback values are accompanied by thick light trails, colored depending on the player that dealt the knockback.
Starting in Brawl, a second formula is also used to alter knockback based on the target's gravity:
The result of this formula increases vertical launch speed if the target enters tumble. As a result, characters with higher gravity get launched faster than those with lower gravity, depending on how vertical the angle is, resulting in fighters with higher gravity stats having worsened vertical survivability, seemingly as an attempt to normalize the effect of combos and multi-hit moves on characters of differing gravity. This formula is also applied to moves that launch opponents downwards, though since vertical launch speed is negative in this case, the result of the formula effectively decreases it slightly instead, reducing the effectiveness of meteor smashes on fast fallers.
In Ultimate, moves that launch at angles between 70° and 110° now instead cause characters' falling speeds to be homogenized to a set value of 1.8. Furthermore, the additional launch speed from the gravity formula is no longer applied. As a result of these changes, falling speed no longer plays as much of a factor on determining a characters' vertical survivability, and moves that deal vertical knockback are generally easier to survive compared to Brawl and SSB4, thus making vertical survivability among the cast much more consistent than in previous games. Note that weight-independent moves do not homogenize falling speeds or use the different gravity value, so gravity and fall speed (especially the latter) still have an impact on the vertical survivability against those moves.
The total amount of knockback dealt can also be subtracted by the target's knockback resistance, which is applied after all the other calculations have been made. However, hitboxes that have the bury effect can ignore the knockback resistance.
If the move has a fixed knockback value set, then d is set to that value, and p is always 10. As a result, the knockback dealt is independent of current damage, damage dealt, and ignores stale-move negation's knockback modifiers. However, it still remains dependent on other factors.
To determine how far a character is launched away, the numerical amount of knockback caused is multiplied by 0.03 to calculate launch speed, and the initial value then decays by 0.051 every frame, so that the character eventually loses all momentum from the knockback. During this time, character-specific attributes such as air friction are disabled; however, falling speed still takes effect, giving fast fallers better endurance against vertical knockback than others of their weight.
Other physics of knockback
Set knockback, also referred to as fixed knockback, is a property of some attacks where the amount of knockback dealt by the attack is always the same regardless of the damage the opponent has received so far, stale-move negation, or how much damage the attack does. Moves with this property can be thought of as those having a knockback scaling factor of 0, though this is actually not the case. Usually, set knockback is used for the first hits of a natural combo or multi-hit move, while the last hit deals normal knockback (sometimes called "scaling knockback" to contrast), to make it easier for the entire attack to hit regardless of the opponent's damage. While damage is not a factor for set knockback, the character's weight still is, so the term weight-dependent set knockback is sometimes used. In Smash 4, the effect of launch rates on fixed knockback was drastically reduced, to the point of barely having an effect at all, while Shulk's Smash Monado Art is ignored entirely. However, other knockback modifiers, such as rage, crouch cancelling, or charging bonus, are still calculated normally. In Ultimate, the effect of knockback modifiers on set knockback was removed altogether.
List of set knockback moves
With the exception of Captain Falcon and Jigglypuff, all characters in Super Smash Bros. have at least one move with set knockback.
From Melee onward, there are certain attacks that deal zero knockback, causing damage as usual but not flinching, meaning that the hit character can still perform any actions while being attacked. Most attacks with no knockback can rack up damage quickly, as they can hit foes repeatedly without launching them away from their range; other attacks that do cause knockback have hitboxes with no knockback in the middle of them for a similar purpose, an example being Roy's Blazer in Melee. These moves can also be used to "steal" KOs from opponents in free for all battles, as while they do not cause knockback, they will take ownership of the KO on an already fatally struck opponent. Fox's Blaster is the most well known example of an attack with no knockback. Due to the fact that it does not deal knockback, it will not interrupt an opponent's moves or force them out of a punishable state such as being asleep or being stuck in the ending lag of a missed Rest. Idle characters in Brawl and SSB4 will also turn around if they are repeatedly struck with moves that deal no knockback, which is noticeable with Fox's Blaster.
In Melee, phantom hits damage foes, but without any knockback. It is also possible for any character to receive no knockback from attacks by certain factors, such as by being giant and metal simultaneously on a low launch rate battle, and as mentioned above, armor will prevent characters from taking knockback while active.
List of moves with no knockback
Introduced in version 1.1.0 of SSB4, certain moves are coded to ignore the target's weight when inflicting knockback, instead using a set value of the default 100. As a result, they are much more consistent across the cast when used as set-up hits and similar.
A few moves not only treat the opponent's weight as 100, but also temporarily set their gravity to 0.085 and falling speed to 1.5, making their knockback even less character-dependant. However, since the gravity and falling speed alterations are temporary, the knockback is still heavily affected by them, and so the vertical KO power of such moves is heavily skewed towards fast-falling characters surviving much longer than heavy ones.
In Ultimate, weight independence is now programmable from a standard flag within hitbox scripts, and as such its effect has been homogenised. If active, all fighters are treated as having a weight of 100 when calculating the attack's knockback, and a fall speed of 1.5 and gravity of 0.087 for the first 10 frames of the launch, before reverting back to a fighter's regular fall speed and gravity. Notably, this effect overrides the homogenised fall speed and gravity used by attacks which have an angle between 70˚ and 110˚.
In addition, all throws in Melee treat the opponent's weight as 100.
Knockback stacking is the means by which knockback is applied to a target that has already been launched by a previous move. Depending on the game and situation, the new knockback can replace the old knockback entirely, have no effect at all, or have its properties merged with the old knockback. In games where knockback stacking is more common, it is an important aspect to consider for combos, as a character will have already been launched when hit by a subsequent move, therefore altering the followup move's properties.
In Melee, knockback stacking occurs if both hits are separated by 10 or more frames, and if the target does not stay on the ground. Otherwise, the second hit's knockback completely replaces the first's. This can lead to noticeable scenarios where strong hits can be canceled into much weaker ones, which is mostly prevalent in team battles or with certain items. This also prevents knockback stacking in cases such as waveshine combos, when a character heavy enough to not be knocked down by Fox's shine is hit back and forth in opposing directions.
Knockback stacking for both hits is done separately for the horizontal and vertical components of their knockback. If both vectors have equal directions on one axis, the stronger component prevails, whereas if they have opposing directions, they are merged via vector addition. This often leads to the resulting knockback having a different angle than either of the previous hits alone. For example, if a character is struck up and right by a strong hit, then up and left by an equally strong hit, the character is sent straight up, due to the horizontal components canceling each other out. In this same example, if the second hit was stronger, the character would be launched up with the second hit's full vertical force, as well as weakly to the left. Knockback stacking occurs even if both hits come from the same character; as a result, there is often residual knockback from a previous hit in a combo, which must be taken into account when trying to follow up.
While knockback stacking alters the resulting angle and launch speed, hitstun always remains the same as if the second hit had struck the target without any merging. However, DI does apply to the resulting knockback vector, so knockback stacking needs to be taken into account for optimal DI. If the victim is grounded and gets spiked towards or in parallel to the ground at non-tumble knockback, they stay grounded, unless the hit also resets.
From Brawl onward, knockback stacking behaves much differently, and its effects have been generally minimized. It now only occurs if both hits come from different sources, and if the second hit's resulting launch speed is lower than 0.8× of the first hit's launch speed at the time the second hit connects. Additionally, the first hit's launch speed and hitstun are retained throughout, instead of being merged and using the second hit's (respectively), and the resulting angle cannot be DIed. Furthermore, if the first hit's launch speed at the time the second hit connects is 2.65× of the second hit's or higher, the second hit's knockback is ignored, though it still applies hitlag. In any other case, the second hit fully overrides the first.
As a result of these changes, knockback stacking is generally no longer a factor for combos from a single character, and it is no longer possible for characters to cancel out strong knockback with significantly weaker attacks. However, hitboxes belonging to articles coded separately from a character, such as Bayonetta's Wicked Weaves, Fox's Fox Illusion, and all projectiles, are considered separate sources, and can thus be subjected to knockback stacking with physical moves from the character that produced them. In Smash 4 and Ultimate, this gives certain characters unique advantages with combo finishers, such as with Robin comboing Arcthunder (in Smash 4) or Arcfire into his down aerial's meteor smash, or Bayonetta comboing her forward smash into her down aerial's meteor smash on a Witch Timed opponent; both of these setups cause the opponent to be launched at a much lower angle horizontally, better securing KOs near the edge if the meteor smash would otherwise cause the opponent to land onstage.
The resulting angle from knockback stacking is determined by the inverse tangent of both hits' added knockback vectors, with the vertical component divided by the horizontal component. For example, stacking Robin's Arcthunder (50°) and down aerial meteor smash (270°) results in an angle of approximately 17.6°. This also means that moves with completely opposing horizontal strengths cannot stack, while moves with completely opposing vertical strengths will result in a perfectly horizontal angle. Worth noting is that when determining whether two moves can stack, the first hit's launch speed takes the gravity penalty into consideration, while the second hit's does not.
The following is a chart demonstrating how much knockback each character sustains in Brawl. While weight is the primary attribute for determining how much knockback a character sustains, there are other attributes that factor in, such as a character's gravity. This results in some characters sustaining more knockback than lighter characters.
The knockback value shown is how much knockback a character sustains when hit with Marth's Critical Hit at 0%, arranged from least knockback sustained to most knockback sustained.