A shield (known as Guard internally) is a bubble of energy that encircles the user. A shield protects the user from a majority of attacks; more specifically, any that are not grabs or determined to be unblockable (including Final Smashes, but not limited to them). The shield is raised by pressing a certain button, which is by default:
Shielding can only be done on the ground; pressing a shield button in midair produces an air dodge instead, or has no effect in the original Super Smash Bros. Shields cannot be held indefinitely; they shrink as time passes and attacks are blocked, and break when held for too long, popping the user up and knocking them down on the ground before stunning them. Otherwise, they recharge when not in use.
Beginning in Super Smash Bros. Melee, shields match the players' colors; they are red, blue, yellow and green respectively for players 1 to 4, while CPUs always have a gray shield. In team battles, non-CPU players' shield colors instead match their team colors, except if team attack is turned on in Super Smash Bros. Brawl and Super Smash Bros. 4 (Brawl also incorrectly gives green team members a yellow shield). In Smash 64, the shield colors are always red, green, blue and gray for players 1 to 4, including CPUs and even in team battles; incidentally, these were the colors used for the players in the game's prototype, Dragon King. In Super Smash Bros. for Wii U, with the introduction of 8-Player Smash, players 5 to 8 have orange, cyan, purple, and slate shields, respectively. Super Smash Bros. Ultimate changes players 7 and 8's shield colors to pink and purple, respectively.
In all games to date, shields come out on the very first frame a shield input is recognized by the game. This makes them extremely fast and reliable for defense, as very few attacks come out as equally fast, and many attacks can be easily punished after being shielded. Due to this characteristic, simply approaching an opponent in a rushed way with a move like a dash attack — a common mistake among new players to the series — is usually an unviable tactic; the player is instead encouraged to win the neutral game by getting in close more strategically, being aware of the different options their opponent has, then attack when they are unable to put up their shields, often by forcing them to commit mistakes or bypassing the shield with a move such as a grab. However, shields in all games are still subject to display lag, meaning they will not be activated at the exact same moment the player presses the shield button; this often causes the impression that an attack was not shielded even though the button was pressed.
As aesthetic indicators, when a shield blocks an attack, it briefly glows and displays a circular graphic in the spot the attack was blocked, alongside a sound effect for blocking. In Brawl and Smash 4, a bit of the shield can be seen visually shattering as well, with pieces flying away, whereas in Ultimate, the shield acquires a checkered texture resembling a white noise image.
Options from the shield
When holding their shield, characters' options are generally much more restricted to compensate for their ability to negate most attacks. If the control stick is tilted slightly, the shield can be shifted to help block attacks from specific directions. If it is tilted faster, the shield is instead canceled into a roll with a horizontal tilt, a jump with an upward tilt (if tap jump is turned on), and from Melee onward, a spot dodge with a downward tilt. In all games except Ultimate, characters can also drop through soft platforms while shielding. These options allow characters to leave the shield quickly, reposition themselves while obtaining some intangibility, or quickly retaliate against an attack, such as an opponent attempting to grab them out of the shield. In Ultimate, if the player holds the special move button, more than one shield button, or (oddly enough) a side taunt input while shielding, these options are disabled, allowing players to shift their shield without accidentally becoming vulnerable.
In all games, grabbing and jumping are other possible options out of shield. Since a grab input in the Smash series is coded as a simultaneous shield and attack input, grabbing can simply be done by pressing the attack button while shielding, and is generally the most basic way of punishing opponents out of shield, known as shield grabbing. Jumping out of shield, on the other hand, grants several more options, allowing characters to immediately use their aerial attacks (including SHFFLing in Melee), wavedash, or jump cancel into their up smash or up special. All these options make shielding the centerpiece to a player's defensive game. Characters can also simply drop their shield and use any attack afterwards, though this causes a short inactionable period, usually known as shield drop lag, while all other listed actions can be done instantly out of the shield. In Ultimate, up smashes and up specials can be performed out of shield without the need of jump canceling, allowing players with tap jump turned off to use them more easily.
While in hitlag from shielding an attack, characters can perform a weaker variant of smash directional influence known as shield SDI, allowing them to adjust their distance from the opponent in order to mitigate shield pressure or facilitate a subsequent punish. Characters can also shield out of a run (but not their initial dash), with a short slide forward due to the remaining momentum, which is useful for faking approaches. In Smash 64 and Brawl, a technique known as dashing shield allows characters to conserve more forward momentum when shielding.
In all games from Melee onward, the amount of health a shield loses when hit by an attack is multiplied by a constant. This constant reduces incoming damage in Melee and Brawl, and conversely increases it in Smash 4 and Ultimate, effectively giving the shield more or less HP than its specified amount. Additional shield damage is also affected by this constant, but not shieldstun or shield pushback.
The formulas are used to calculate the initial amount of pushback, which is then decayed every frame by the character's traction value. From Brawl onward, both characters' traction is multiplied by 1.1× until the pushback ends.
Worth noting is that while the defender's shield pushback has a cap in all games, the attacker's does not. As a result, if an attack that deals extremely high damage is shielded, the attacker can be pushed back with enough strength to be forced off the stage and get KO'd; the Kamikaze glitch is an example of such a scenario. In Melee, attacker shield pushback can also cause the ceiling glitch.
Analog shield data (Melee only)
Several shield properties in Melee are altered if the L or R buttons are not fully pressed. Put in simple terms, lighter shields are larger and take longer to deplete, but take more damage, and increase the defender's shieldstun and pushback, while reducing the attacker's pushback. As a result, they are safer to use preemptively and can prevent shield stabbing much more reliably, but are significantly less effective for subsequent retaliation.
In all formulas, s is an analog factor equal to
Shields are larger the more health they have remaining, in addition to each character having their own shield size ratio. As the shield is raised and blocks attacks, it keeps diminishing until it breaks. This phenomenon is known as a shield break, and results in the character being launched a distance upward, getting knocked down as they land, then being stunned for some seconds after standing up.
The purpose of shields breaking and diminishing is, along with grabbing, to prevent players from protecting themselves indefinitely. Instead, as the shield gets smaller, a larger portion of the character's hurtbox is left vulnerable to attacks. Shield breaking is commonly done either by taking advantage of shieldstun to chain several attacks with little room for the opponent to escape, or by landing attacks that deal high enough shield damage, such as Marth's Shield Breaker or throwing Mr. Saturn.
Shield breaking is especially dangerous at the edge of a stage, as due to shield pushback from the move that broke the shield, the character can get pushed off and continue falling until they reach the bottom blast line, leading to an inevitable KO. Jigglypuff is also affected more severely by shield breaking, as unlike other characters, it is launched several hundred times farther upward than normal, which is more than enough to KO Jigglypuff unless there is an overhead obstruction (in which case, it will helplessly keep trying to float up until several seconds have passed, the obstacle is removed, or Jigglypuff is smacked out of it).
Players who use Rosalina & Luma are still able to control Luma's attacks even if Rosalina is stunned from a shield break.
Characters with unique shields
In all games, Yoshi is notorious for having a unique shield from every other character. Instead of using a bubble, he curls up inside a Yoshi Egg that does not shrink. Instead, as the shield weakens, the egg gradually acquires a darker tint until becoming completely black, similarly to the effect used by players' damage meters as their percentage increases. This is generally an upgrade over other characters' shields, as it effectively renders Yoshi immune to shield stabbing (except in Brawl, where a small part of his feet's hurtboxes still poke out of the shield), and eliminates the necessity of shifting the shield; however, it also has the disadvantage of his shield being easier to break, leading to a potentially more severe punish than if he merely got shield stabbed.
Depending on the game, Yoshi's shield also has several different properties from other characters' shields, both positive and negative.
In Smash 64
In Smash 4
In Ultimate, due to the changes to shield time and the removal of shield platform dropping, Yoshi's shield no longer has practical differences from the rest other than its fixed size, making it generally more advantageous.
While Jigglypuff uses the same bubble shield as other characters, its shield jump in all games is uniquely more punishing. The force Jigglypuff is sent upwards with if its shield breaks is equivalent to taking 300 units of vertical knockback, which is more than enough to cause it to self-destruct if there's no overhead obstruction. However, this can also be useful for certain situations in single-player modes, such as the Brinstar Escape Shaft in Melee's Adventure Mode and The Glacial Peak in the Subspace Emissary.
Unique actions out of shield
In Ultimate, while Inkling and Steve's shields are identical to other characters', they have access to unique actions by pressing the special move button while shielding. Inkling changes into squid form and recharges ink from the ground, then changes back to normal after completely refilling the Ink Tank or if the button is released. On the other hand, Steve summons his Crafting Table to his current location, at the cost of some materials. This aids both characters with their respective fighter abilities, allowing Inkling to regain ink for attacks that utilize it, and Steve to use his Crafting mechanic more conveniently. However, these actions cause them to leave the shield and thus become vulnerable to attacks, although Inkling still has a reduced hurtbox size while recharging ink.
Since these actions are performed with the special move button, Inkling and Steve players can only use the "shield shift lock" feature by holding multiple shield buttons or a side taunt input. Oddly enough, this also applies to Snake, despite him having no unique shield actions.
The concept of blocking attacks is a standard amongst the fighting game genre. In traditional fighting games, blocking involves characters bracing against attacks (such as by holding up their arms), which typically prevents the character from flinching or being affected by any of the attack's effects or gimmicks. Blocked attacks may still deal minimal damage referred to as "chip damage" depending on the game and/or type of attack blocked (normally applies to damaging special moves), and blocking too many attacks can break the character's guard and leave them vulnerable. Many fighting games require players to choose between blocking high or low attacks and do not allow players to block grabs or attacks from behind.
In Kirby Super Star, Kirby is capable of blocking attacks in a way reminiscent of most traditional fighting games—protecting him from flinching or losing his ability while still dealing minor damage if the attack is strong enough—though he automatically guards from all directions. In addition, if Kirby has the Mirror ability, guarding produces a multi-colored bubble around his body that blocks all non-grab attacks without chip damage and is even capable of reflecting certain projectiles. It is this bubble that appears to be the inspiration for the shield bubble in the Super Smash Bros. series. The Smash Bros. bubble would later make an appearance in Kirby's Smash Bros ability in Kirby: Planet Robobot, functioning identically to that of the Mirror ability.
Yoshi's shield design, on the other hand, is possibly based on an occurrence in Super Mario World 2: Yoshi's Island. When Baby Mario grabs a Super Star and starts running around, Yoshi follows by hiding in an egg and becoming part of his egg trail. The duo is invincible during this time. The shield may also be based on Yoshi becoming invincible once swallowing a Turbo Tulip in Yoshi's Story, although that is generally attributed to the Egg Roll instead.
Inkling's method of refilling ink is based on Splatoon and Splatoon 2, where the player's ink can be refilled by becoming a squid and diving into ink of the same color. In these games, becoming a squid is mapped to the ZL button; the ZL and ZR buttons shield by default in Super Smash Bros. Ultimate.