Launch rate, also known as Damage % in Super Smash Bros. and Damage Ratio in Super Smash Bros. Melee and Super Smash Bros. Brawl, is a feature in all Super Smash Bros. games that alters how much knockback is given and received (despite the name in Melee and Brawl, damage is unaffected).
All knockback in a match is multiplied by the launch rate value, which by default is 1.0×. With the setting, this can be set from as low as 0.5× (attacks have half knockback) to as high as 2.0× (attacks have double knockback). The minimal launch rate is ideal for combos, while the maximum launch rate is ideal for KOing opponents at extremely low percentages. However, the latter also affected attacks with set knockback up until Smash 4 and Ultimate, causing multihit attacks to not always combo into each other.
In Competitive Play
There has been some discussion among Brawl's competitive community as to whether using a launch rate value other than the default 1.0 results in a more healthy metagame; 1.1× is a commonly-mentioned value claimed to make many polarizing attack chains (such as using Sheik's forward tilt into itself endlessly) less viable while also shortening the length of stocks. The idea has never attained serious consideration among tournament organizers.
In tournament play, nonstandard launch rates are difficult to detect during games, which has led to some tournament matches unintentionally having been played at an incorrect launch rate. A notable example of this was a set between Armada and SilentSpectre at Pound 4 in 2010 that was played at 0.9×; this remained undiscovered for nine years.
Some of the more recent, infamous examples are the games between komorikiri and CaptainZack, and ZeRo and Dabuz at GENESIS 4. Both were being played at a setting of 0.9×. The latter gained notoriety, and soon became an inside joke in the community.