A counterattack is a type of special move. Debuting in Super Smash Bros. Melee, a counterattack will, on use, put the user into a shield-like state followed by a sizable period of lag. Should any normally blockable attack hit the user during these guard frames, the attack will be blocked (without depleting the health of their shield) and the user will automatically retaliate with an attack of their own, presumably hitting whoever was attacking unless it was a projectile, or some other attack that out-ranges the counter.
Some counterattacks do more damage when they activate against a stronger attack, with knockback scaling to match the damage, while some deal a fixed amount of damage. Counterattacks usually activate fast enough that it is impossible for a melee attacker to shield the retaliating hit, although the attack itself can usually be blocked; there are a few exceptions, such as Shulk's Vision in Super Smash Bros. 4, which is unblockable. Counterattacks also do not trigger if the fighter is invincible, even if the opponent hits them. The animation will simply play as if they were not hit at all.
A correctly-timed counterattack can tilt the momentum of a match towards the user, though as they are generally not effective on reaction, reading the opponent is crucial. Simply using counters repeatedly in hopes of successfully landing one in will result in a competent opponent waiting until the move's lag to attack, or simply using a grab, which is immune to counterattacks.
While unblockable attacks cannot be countered (except with Witch Time), as previously mentioned, depending on the move, the user may still not receive damage because of the initial invincibility frames. Unlike reflectors, there is no limit to how much damage can be countered. In SSB4, however, there is a cap on how much damage a counterattack can inflict, at 50%. The only exception is Shulk's Vision; its damage cap can be raised or lowered depending on which Monado Art is currently active. In SSB4, counterattacks also cannot counter some explosive attacks, such as Link's Bombs and Steel Diver missiles, and instead give the user protection against them during the counter frames. Stronger explosions can be countered, however, such as the Bob-omb.
Prior to SSB4, counterattacks lacked any special aesthetics upon activating. In SSB4, most counterattacks, upon activating, emit a unique particle effect identical to a sinus rhythm. This applies to all counterattacks lacking a separate particle effect, namely the entire cast that possesses a counterattack, save for Greninja and Lucario. Each counterattack's sinus rhythm is distinct (ex. Palutena's is blue, Little Mac's is red, etc.). In Super Smash Bros. Ultimate, an additional visual effect occurs if a strong enough attack is countered, with the user emitting a large, bright yellow flash.
List of counterattacks
Counterattacks only available as custom moves are in italics.