Frame delay

Frame delay is the time difference between an input being given and the result being executed in an online game. In other words, it is the amount of time it takes for an attack to actually begin after the button has been pressed.

Overview
The player's system must send what their input currently is every frame (60 per second in the Smash series), so that the other systems can know what to do. However, communication between systems over the internet is not instantaneous. If at least one system has not received the input yet, the game must wait until it gets the input, causing lag. The game attempts to compensate for lag and make it feel less noticeable by intentionally not acting upon the input for a few frames; this is the frame delay. After the number of frames that the frame delay specifies, the input is acted on.

Frame delay is often confused with Wi-Fi lag, though it is in fact closely connected with it. Frame Delay is intentionally created by the developers to mitigate and hide unintentional aspects of gameplay Wi-Fi lag. While it's possible to have no lag in a match, frame delay will always be present, even if by a tiny amount. This makes online matches much more prediction-driven than their offline counterparts.

Brawl Wi-Fi lag
Brawl wifi also shows the extent of frame delay. At the side of every person registered using friend codes, after completing at least one match and quitting (not restarting), a large dot will show up, being colored. This dot refers to the person's connection. The color coding from best (3 frames) to worst (more than 15 frames) is as follows:
 * Dark blue
 * Light blue
 * Green
 * Yellow
 * Orange
 * Light red
 * Dark red

Server play
Server frame delay is due to the distance between a person and the server. There are 6 different connection types which can change a person's delay. These connections vary due to the amount of packets. At the start of going on a server, it automatically sets the lag to good but the majority of people who play Smash 64 often are using excellent or LAN connections. These different connections cause different strains on the computer. These connections in other words are better for the higher packet numbers but it takes a larger strain on the computer to run. A connection below 30 ping on an excellent connection, for example, has 3 frames of delay while a connection below 30 on LAN has 1 or 2 frames of delay (1 below 15) while the same connection on good has 5 frames of delay. The majority of people who are used to online Smash can reasonably play on any connection that is better than 6 frames of delay. Excellent is the most common connection since LAN causes problems with some players online.
 * LAN 60/s
 * Excellent 30/s
 * Good 20/s
 * Average 15/s
 * Low 12/s
 * Bad 10/s

Player to Player (p2p)
Player to player, which connects one person's connection entirely to another person's connection reduces the amount of delay between players. This is very common to be used between 2 people on opposite coasts, or between a US and a European smasher.

Super Smash Bros. 4
In Super Smash Bros 4, seven frames of delay between pressing the button and the game actually outputting the respective action are always present, regardless of gameplay mode, although slower monitors have more input delay.

Super Smash Bros. Ultimate
In Ultimate, roughly six frames of delay between pressing the button and the game actually outputting the respective action are always present regardless of gameplay mode, marginally less than Smash 4. The issue of slower monitors having more input delay still exists.

In competitive play
Frame delay is a controversial conversation in the Smash series, particularly with Smash 4 and Ultimate. Frame delay was not considered a big deal in Brawl due to being exclusive to online modes that were already problematic and offline tournaments reigning supreme at the time. Smash 4 applying delay to the entire game, including offline modes, was met with considerably more hostility. Some saw this as a lazy way to address players with poor online connections by punishing everyone else until everyone is at an even playing field. Another concern is the delay objectively making reaction times slower, making certain interactions theoretically possible but mathematically impossible to react to. Others saw this implementation as ultimately necessary, as it would make the transition from offline to online less jarring and would make online an overall smoother experience. Ultimate reducing the delay was met with slightly positive reception, though many still say the delay is too extreme and needs to be lowered further.