Freeze frames (also known as hitlag or hitstop, and officially known as hitstun) are a phenomenon that appears in all games of the Super Smash Bros. whereby a character will freeze for a period of time after connecting with an attack. If successful with most attacks, both the attacker and target are frozen in time for a number of frames. This causes the attack to get "stuck" out longer than it would if it had not hit anything, while the target has a short time to react before the knockback occurs. This is most easily noticed in multi-hit attacks such as Yoshi's down aerial; the attack takes less time to finish if it does not hit anything. Once the freeze frames have passed, both sides resume action. During freeze frames, defending characters are capable of performing smash directional influence to get out of combos or multihit moves, or to increase their chance for survival.
The formula for calculating the freeze frames experienced by both the attacker and victim has been different for most of the games:
For all these cases, the final result is rounded down. d is the amount of damage an attack would deal, ignoring stale-move negation for Melee, while m is a series of multipliers based on certain factors, including:
As shown by the formulas, the general amount of freeze frames on moves is at its lowest in Melee, and has since increased throughout the series, with Ultimate having the most freeze frames. In all games, freeze frames are higher the more damage a move deals. For example, weak attacks such as Mario's jab have minimal freeze frames, but the freeze frames of strong or sweetspoted attacks can last as long as half a second. In addition, Brawl introduced the mechanic of hitlag modifiers, causing variance in the freeze frame duration of attacks; this is in contrast to Melee and Smash 64, where the duration of freeze frames was predictable.
Freeze frames are also exaggerated if two attacks clash, or the attack is perfect shielded. In the latter case, the attacker suffers from hitlag while the defender receives none. Also, if the attack doesn't deal more than 0 units of knockback, the target will never be affected by hitlag.
Freeze frames only affect the object that deals the damage. All other game elements (including, interestingly enough, any particle effects the attack generated) are uninterrupted. For example, both Captain Falcon and his opponent will undergo freeze frames upon a sweetspotted Knee Smash, while Samus' movement is not interrupted by a Charge Shot hitting someone, since it is a projectile not attached to her. Freeze frames do, however, affect attacks that have disjointed hitboxes. Freeze frames affect the attacker as long as the attack connects, even if it deals no damage as a result of hitting opponents with invincibility.
Electric attacks have a special effect on freeze frame duration. The amount of freeze frames inflicted by attacks with the electric effect is multiplied by 1.5 (rounded down), and said multiplier stacks with the hitlag multiplier that the move otherwise has (i.e an electric attack with a hitlag multiplier of 1.2 would actually deal 1.8 times the amount of freeze frames). Interestingly, if a fighter is hit by an electric attack from another fighter, and either the target fighter or both fighters are affected by slowdown (e.g by the timer item), then the target fighter will receive additional freeze frames, while the attacker will not. This phenomenon does not occur with non-electric attacks, even those that have a hitlag multiplier.
Hitlag is a mechanic that was borrowed from traditional fighting games.