The crowd, referred to as Publicity in the debug menu of Super Smash Bros. Melee, is a group of unseen people that can be heard during matches in all games of the Super Smash Bros. series.
Causes of cheering
The crowd can occasionally be heard cheering by shouting the name of a character that is used by a human player. The cause of cheering, however, is not entirely known; common trends include having high damage, the start of the match after the announcer gives the "GO!" signal, and doing something significant, such as KOing multiple opponents at once, or falling behind considerably during the course of a match. Every character has a unique cheer chant in each of the Smash Bros. games.
In addition to chants, the crowd can also vocalize during the match to a variety of events. In the original game, if a player can just make it back to the stage, after being knocked far away from the stage, the crowd will cheer for the player. The crowd also cheers if Ness absorbs a projectile with PSI Magnet, as well as if a character hits multiple characters or lands a powerful hit. Since Melee, the crowd will gasp if the player gets close to the ledge after getting knocked off; they will also cheer loudly if the player hits multiple opponents with a powerful attack. In addition, in Melee the crowd cheers the player if they complete the Target Test, complete an Event Match or the Race to the Finish. However, they will groan should the player fail at any of these games. In Brawl and SSB4, the crowd will also gasp whenever a Smash Ball or legendary Pokémon appears, with the exception of Latias and Latios. In SSB4, the crowd will groan if a player finishes with no points in the Home-Run Contest or Target Blast. In all games except for SSB4, the crowd will be silent during Sudden Death.
Despite their presence, the crowd has no effect on gameplay. A sole exception exists in the Bonus mode of Melee; if the player earns the "Crowd Favorite" bonus from getting the crowd to cheer for them, or the "Master of Suspense" bonus from causing the crowd to gasp at them at least three times in one minute, they will earn 2500 points from each.
Of further note, the crowd seems to "disappear" after a certain point is reached in some of the single player modes. In Melee, the crowd disappears starting at Race to the Finish and at Stage 12: Final Destination in the Adventure Mode. In Brawl, the crowd disappears during the fight against Master Hand, and is only heard when certain stages are cleared in the Subspace Emissary. In SSB4, the crowd disappears during the fight against Master Hand and, if applicable, Crazy Hand and Master Core.
Certain characters have noticeably different names in Japan (such as Jigglypuff as Purin and R.O.B. as Robot); their names are adjusted accordingly in the cheer.