Grab release is the animation that characters enter when they are freed from a grab without entering knockback. Normal grab release occurs after a certain amount of time if a grabbed character is not thrown (this time can be shortened by button mashing), but characters also enter grab release when the grabbing character enters hitstun or the platform they're standing on disappears. There are three main types of grab release animations: ground release, air release, and pummel release. Many combos can be performed by attacking when an opponent is stuck in the frames of their grab release animation. There are no grab releases in the original Super Smash Bros., where waiting too long will just result in a forward throw. The exception is Donkey Kong, whose forward throw can be mashed out of.
Types of grab release animations
Ground release is the animation a character enters when they break out of a grab sliding backward along the ground, along with a "letting go" animation. The grabbing character may slide backward a bit as well. The distance sent is affected by the grabbing character and the victim's traction. A ground release causes both characters to be stuck in 30 frames of ending lag where they cannot react, with a few exceptions (see below). A ground release occurs when the grabbed character's feet are touching the ground and not moving around while being grabbed.
Air release is another animation a character can enter after escaping from a grab. In an air release, the grabbed character performs an arch-like movement backwards into the air, along with a "letting go" animation. In Melee, the direction the grabbed character moves can be altered slightly by pressing left and/or right. The distance sent is character-specific and can be affected by air speed, falling speed, and falling acceleration. An air release causes the grabbing character to be stuck in 30 frames of lag, but the victim is stuck in 50 frames of lag, with a few exceptions (see below). In Brawl, an air release will always occur if the victim's feet are not touching the ground, but the grabbed character can force an air release (even if their feet are touching the ground) by pressing the jump button or up on the Control Stick shortly before being grab released. In Melee, an air release will only occur if forced. Taller characters tend to be able to air release more characters and are more vulnerable to ground releases, and shorter characters tend to be able to ground release more characters and are more vulnerable to air releases. However, the grabbing height of a character can be different depending on the direction they are facing, as well as whether a standing grab, dash grab, or pivot grab is used; a character could be air released facing left and ground released facing right, and vice versa. Despite having a 20-frame disadvantage, only a few characters can be affected by grab release combos since the victim is usually sent away from the opponent.
The pummel release is a type of grab release very similar to the ground release, but it occurs when the grabbed character is pummeled right when or right before they are grab released. A pummel release can occur even if the character would normally be air released, and a pummel release cannot be forced into an air release by pressing up or jump. The distance sent by a pummel release can be different than the distance sent by a ground release, as a pummel release will cause normally air-released characters to fall to the ground without sliding backward.
Other grab releases
When the grabbing character and/or the victim enter knockback, the victim will receive an additional 3%. If only the grabbing character is hit, the grabbed character will also enter an animation similar to a ground release.
If the platform the grabbing character stands on disappears, the victim will receive 3% damage and the grabbing character will be sent away in an arc similar to an air release.
If the grabbed character is lifted up by the platform they are hovering over, they will eventually break apart from the grabbing character and both characters will enter an animation similar to a ground release.
Notable grab release combos
Both chaingrabbing and grab release combos have been mostly removed in Smash 4 due to some core game mechanics being changed. However, there is a few select exceptions.
Grab releases in the original Super Smash Bros.
Grab releases do not exist in Smash 64; a grab always lasts the same amount of time, and once that time is up, the character will automatically use a forward throw. Grabs cannot be mashed out of in this game, and the only way to escape grabs is if the victim is hit hard enough by a bystander's attack, in which case they will take the knockback of that attack. Donkey Kong's cargo release available in his forward throw may be considered a pseudo-grab release, due to DK losing hold of the opponent so they are vulnerable in front of him for a few moments (allowing techniques such as the infinite throw trap), but it is more of a way the throw works rather than an actual grab release.
It is currently unknown why Ness, Lucas, Jigglypuff, Bowser, and Donkey Kong have different grab release frames from the rest of the cast in Brawl. It is commonly believed that this was done to intentionally buff or nerf these characters, but there is no evidence supporting this, and many have stated that this is not an effective way to buff or nerf the characters.
The usage of grab release combos in tournaments has also been debated. Many claim that exploiting grab releases is an unfair disadvantage for the affected characters, as many of these combos can lead into guaranteed KO moves, and some are even zero-deaths and infinites. Grab release combos have been cited as the reason for Ness's and Lucas's lower tier placements throughout Brawl's history, and zero-death grab release combos in particular have been criticized for making certain matchups nearly unwinnable for affected characters. Others however, have argued that grab releases are a part of the game that must be dealt with and are an inherent strength/weakness to characters affected by them, and that they aren't functionally different from standard combos.
There have been some tournaments that have banned these grab release exploits (typically the grab release chain grabs on the PK kids), though this rule occurs only in fringe locals and has never been implemented in more major tournaments, as competitive players generally maintain that all techniques are fair game to use unless demonstrated to be broken. They also maintain that tournaments should be discouraged to implement rules just to arbitrarily buff or nerf certain characters and that "complex bans" should be avoided.
However, while competitive players generally accept grab release exploits, they generally don't like them, and as such, all the major Brawl mods have made efforts to remove all potential grab release followups.