For whatever reason there's a dance or a dinner, or a party of some kind, going on — be it a snooty royal or noble ball, a school dance or a wedding, or maybe a particularly large birthday party. If it's a more formal occasion, pretty much everyone is dressed up. There's a fairly good chance that if our heroes have been invited, the Big Bad or his mooks are quite likely to invite themselves; be assured something catastrophic and violent is going to occur, usually in the vicinity of either the entrance or the dance floor. In most circumstances everyone will be unarmed, except maybe the guards (if they even have them). Cue panicked screams, and the Action Girl complaining about having to fight in a dress... until she rips the hem off. May overlap with A Fête Worse than Death — or, in a comedy, Hilarity Ensues. Compare Wedding Smashers. If the hero is wealthy enough, he may end up Paying For The Action Scene out of generosity.
An early episode of Mobile Suit Gundam Wing had Lady Une try to assassinate Relena during a school formal, which lead to Heero going out and fighting them off in his Gundam. No fighting actually occurs inside the party, though.
In the manga version of Mahou Sensei Negima!, Ala Alba kicks off the blitz during Negi's escape from the governor's office. Unfortunately this coincides with the arrival of Cosmo Entelecheia...IN FORCE. Looks like that's it for tonight's dances of romances.
Yu-Gi-Oh 5Ds: Some duelist on a giant spiked bulldozer crashes some fancy party during the WRGP Arc. Aki ends up summoning her dragon and tossing him through a window.
Towards the end of the Baccano!! arc set in 1930, Szilard tracks down Maiza at the party to celebrate Firo's entry into the Camorra. Machine-gunning ensues. Unfortunately for Szilard, it generally fails to stick.
In The Big O, Roger gets invited to a masquerade ball and is given a mask to wear. Roger chooses not to put it on—good thing too, because Schwartzwald had booby-trapped the masks to spontaneously combust, turning all of the other attendants' faces, all of them high society people, into charred messes.
Pretty much guaranteed to happen at any superhero wedding. Notable examples include:
In the Batman story arc Lovers and Madmen, the villain Jack aka the soon-to-be Joker attacks a Museum Charity Ball to get Batman's attention.
In the first arc of Grant Morrison's Batman, Batman and Son, a bunch of ninja Man-Bats attack a charity ball in London.
In Naruto Veangance Revelaitons, while Ronan and Sakura are attending the "sibone ball," Madara attacks. Ronan defeats him by mind controlling the attendees.
Subverted in the The Game of Three Generals, the third part of the Elemental Chess Trilogy. Grumman and the allies throw a ball hoping to lure Acheron into attacking, but nothing happens, making them even more anxious.
As the Mistress is going through contractions in Chapter 13 of the Superjail! fanfic Extended Stay while she and the Warden are getting married, the inmates start to riot, even killing the priest in the process. Alice and Bruce are the only ones to be able to put an end to it.
Another example of this occurs in Chapter 7 while the Warden and the Mistress are on a date.
In Night of the Creeps, the dance never happened because the busload of fratboys all died due to the eponymous monsters and the undead serial killer.
The big fancy ball in Enchanted gets interrupted due to Nerissa first pulling the poison apple thing on Giselle, and then turning into a dragon. Also makes use of All Part of the Show.
Carrie 1976 climaxes at the prom, where a cruel prank causes Carrie to go on a rampage and kill everyone.
Averted in West Side Story, where there is racial tension at the dance, but the gangs wait till afterward to rumble.
Nigh of disco dancing is ruined in Prom Night 1980 when the killer makes himself known during the crowning of prom king and queen.
Batman Returns: The fancy costume party at which Bruce and Selina discover each other's identities gets interrupted explosively by the Penguin.
Batman Forever: Two-Face crashes Edward Nygma's (The Riddler's) party despite the two working together. Followed soon after by Batman.
Riddler: Your entrance was good; his was better. The difference? Showmanship.
Batman & Robin: Bruce organizes a charity auction sale of diamonds in order to lure Mr. Freeze. Poison Ivy infiltrates the party in a pink gorilla costume, takes it off and seduces everybody with her love perfume, then Freeze crashes the party.
Batman Begins: Rā's al Ghūl and his men crash Bruce Wayne's birthday party.
The Dark Knight: The Joker and his men storm Bruce's fundraiser as they try to assassinate Harvey Dent, having succeeded in eliminating Commissioner Loeb and Judge Surrillo. This is why Bruce can't have nice things.
Averted in The Dark Knight Rises: Bruce Wayne does go dancing with Selina Kyle at a ball, but Bane does not attack.
Van Helsing: The All Hallow's Eve Ball, which quickly erupts into a battle with Dracula.
In Swing Kids, one swing dance party gets raided by the Hitler Jugend, leading to pandemonium as everyone tries to escape out the back. At the end of the movie, the Hitler Jugend raid another swing party, this time more prepared to apprehend everyone there. It does not end well for the partygoers.
Daywatch has Yegor's birthday party, organised by the Big Bad and attended by many high ranking Others (and several Russian celebrities in Cameo). Everything goes well, if tense, until Yegor's estranged father, Anton, bumps into a Witch he arrested years ago. A scuffle erupts, turns increasingly violent and climaxes with someone throwing a magical frag grenade that destroys Moscow.
Brave — The three lords and their clans gather at the castle to participate in the Highland Games. During the formal presentation of their sons in the throne room, a massive fight occurs. Fergus makes a feeble attempt to restore order before diving into the fray, leaving his queen Elinor to restore order.
Die Hard, Hans Gruber and his terrorist interrupt the Nakatomi companies Christmas party to take everyone hostage.
In The Avengers, Loki disrupts a very formal party in Germany in order to use one of the guests' eyeballs to allow the corrupted Barton to break in and steal something.
In Fiddler on the Roof, the party celebrating Tzeitel and Motel's wedding is rudely interrupted by the Cossacks, who attack without warning.
In The Silmarillion, Morgoth attacked Valinor and seized the Silmarils during a festival. Gondolin also fell during a festival when none of the walls were manned.
In Cluster Command the second book of David Drake's Crisis of Empire trilogy protagonist General Merikur and his wife Beth find themselves in the middle of such a blitz at the welcome ball for the new system governor.
The Dresden Files book Grave Peril has Harry winding up attending large party being thrown by a vampire. It winds up being an example of why villains request his presence at their own peril.
Nanny Ogg's Cookbook: "The Fight" is listed as part of a proper wedding. The last step is "Then the bride cuts the cake."
Night Watch: The Patrician's party. Though no actual violence is employed (save for two guards who took crossbow bolts); the Patrician (Lord Winder) is literally scared to death by a young Havelock Vetinari.
The final confrontation between Granny Weatherwax and her sister of Witches Abroad takes place in an elegant ball.
In By the Sword, Kerowyn is first thrust into her role as Action Girl when mercenaries ransack her brother's wedding, kill her father, and abduct the bride.
Of course, Bill and Fleur's wedding in Harry Potter and the Deathly Hallows. Even more so in the film, as in the book our three heroes manage to escape within a very short time after the villains' interrupt.
Live Action TV
Minutemen has a dance interrupted by a black hole.
Heroes has Claire's big homecoming dance interrupted by a Sylar attack.
In Merlin the two-part finale of series four begins when Morgana and her mercenary army attacks Camelot during the Beltane celebrations.
in an episode of Monty Python's Flying Circus, a bunch of nobles at a fancy ball are consistently interrupted by highwayman Dennis Moore.
The Trope Namer is "Ballroom Blitz" by Sweet. It is a surreal and lighthearted description of such an event. Covered by lots of people: The Rezillos, The Damned, and by Tia Carrere on the Wayne's World soundtrack.
It was inspired by a gig gone wrong in Scotland in 1973, when the band was showered by bottles from the audience and had to leave before finishing the set ("And the band started leavin'/'Cause they all stopped breathin'").
The Julie Brown Song "(Everybody Run) The Homecoming Queen's Got A Gun" involves an interrupted homecoming parade.
The Irish folk song "Lanigan's Ball" (given a Boston twist by the Dropkick Murphys as "Flannigan's Ball") is about one of these.
The Karazhan raid instance in World of Warcraft has a variation. One section of the dungeon involves going through the ballroom and dining room, which are filled with ghosts. The ghosts are acting as people normally would, dancing and eating, with servants walking among the tables in the dining room. Of course, the players have to fight these ghosts to continue.
One mission in Assassin's Creed: Brotherhood turns into this. A Borgia cardinal is throwing one hell of a party, only for Ezio Auditore da Firenze to crash the party and murder the cardinal. Subverted in that all of the guests make it out just fine. The guards, on the other hand, are pretty much boned.
The boss fight of your first visit to the Beauty and the Beast level of Kingdom Hearts II takes place in the iconic ballroom. By your second visit, they've got around to the actual dance scene - but it's interrupted by Xaldin, who kidnaps Belle and lures everyone outside.
The first episode of Freakazoid!, "The Dance Of Doom" has a high-school dance interrupted by Cave Guy, who takes several of the high-schoolers hostage. Of course, this being Freakazoid, the dance is in honor of Daylight Savings Time.
An episode of Teen Titans in which Robin is forced to take a supervillain's daughter to her prom ends up this way when Starfire's jealousy flares up and said supervillain's daughter's ex-boyfriend (who turns into just plain her boyfriend again shortly before the actual Blitz part of it starts) shows up.
Danny Phantom: In the second episode, Danny decides to take some inconspicuous ghost-fighting weaponry to the school dance "just in case." Case happens.
American Dad!: In "Haylias", after Hayley's arranged marriage is consummated, she attempts to murder Stan during the wedding party. Part of the scenes is a Shout-Out to Carrie.
In the X-Men: Evolution episode "Shadow Dance", where the monsters that inhabit the pocket dimension Nightcrawler crosses every time he bamfs from one place to another manage to escape and start making a rampage in Bayville High, during the Sadie Hawkins dance night. Being this the school that the X-Men and the Brotherhood attend, they have no problem dealing with them. Kurt, on the other hand, is afraid of doing anything, both because said monsters had traumatized him earlier on (to a point he swore to himself he would never teleport again) and because he didn't want Amanda to find out he was a mutant. Turns out she already knew about his powers and his true appearance, and he manages to teleport them both out of school in the last minute at her urging.
This happens again in the season 2 episode "Sweet and Elite", when the main cast invite themselves to a garden party Rarity had been secretly attending. Fortunately, the end result is somewhat more positive this time around.
In fact, the first example arguably happens right in the two-part pilot with Nightmare Moon crashing Ponyville's Summer Sun Celebration.
It happens yet again in the second season finale, when a wedding between Princess Cadance and Shining Armor is interrupted by Twilight Sparkle and the real Cadance. The fake Cadance reveals her true form as queen of the Changelings, and her minions proceed to besiege all of Canterlot.
Subverted in Reboot. For Enzo's birthday, a surprise party/talent show is planned. Villain Megabyte keeps menacing Bob during the preparations. At the actual party, after the comedy acts, Dot singing a torch song, and other festivities, Megabyte barges onstage — with an electric guitar. He plays power chords while his dimwit sidekicks Hack and Slash back him up on drums. Bob pulls out HIS guitar, and the two jam with each other! Megabyte's actual plan? "I've always wanted to do that!" He gives his guitar to the birthday boy, gets in his limo, and leaves.
Superjail!: In "Ladies' Night", this occurs at the Warden's "Lockdown of Love" after Superjail's Distaff Counterpart is bitten by Spanish Flies.
Archipelago: Book 6, Snow and the Ravens attack Quillotia Castle during a royal ball. As far as King Mikel is concerned, this does not ruin the evening.
RPG World contains one of these in the Elven village, Chery's hometown.
In The Gamer's Alliance, the Maar Sulais court has a grand ball in honour of the Grand Alliance army which has come to join them in the fight against the Proninist Party. However, just when festivities are about to reach their peak, the Nightstalkers gang crashes the ball in the citadel, causes general havoc and kidnaps the elven mage Tiyana before the heroes can stop them.
The Gungan Council has frequent dances and balls, so the Sith decided to host their own called "The Homecoming Ball" and invite Jedi and Rebels. Nowadays, its nickname "The Blood Ball" is known much more than its true name.
There is a joke in Finland about the stereotypically stern, quickly aggravated, knife-wielding Ostrobothnians.
Q: "Why are the floors of dance halls in Ostrobothnia built to have a slope?"
A: "So that the blood will run off better."
When people objected to weddings in the Middle Ages, it was not unusual for it to end violently. Hence, the title of "Best Man" usually referred not only to trust or friendship, but fighting ability as well.
In certain remote rural districts, this tradition has allegedly persisted into the modern age.