The heroes entered the classical old pub, saloon, or roadside bar, probably looking to relax. Normally, a particularly nasty guy taunts one of the characters and tries to hit him. Sometimes it connects. Other times, the hero is able to duck, and the other guy hits a bigger, nastier guy who proceeds to toss him against a table, causing the people sat at that table to react, and soon enough three quarters of the customers are tangled in a chaotic battle, throwing chairs, bottles, and tables and resorting to dirty fights. You get the picture.
This trope tends to be quite common and is often paired with Bar Brawl with some exceptions. The focus point is that it starts as a duel and ends up growing and dragging along other characters, like an avalanche. In westerns this tends to be quite common. Especially funny if the participants just start fighting each other for the hell of it, even if they have no grudges against each other. Sometimes even if they are friends!
- In Fairy Tail, the first time we see the titular guild, Natsu causes one of these. Luckily, Makarov stops the brawl before anyone resorts to magic.
- In Dragon Ball Insanity School at the end of the World Tournament Vegeta, angry against Trunks hits him, prompting Pan to come to his help and getting hit, prompting Gohan to join the battle, prompting Trunks to protect his father, prompting Goten to defend his brother, prompting Vegeta to protect his son and finally pushing Goku to help his sons.
- The brawl in chapter 31 of Earth and Sky stars with Applejack confronting Baron Redtail and kicking one of his bodyguards into a crowd of angry ponies threatening the Flim-Flam brothers over all the cheating they've been doing. Things sort of escalate from there.
- The Great Race
- In the town of Borracho, a fight between The Great Leslie and Texas Jack quickly turns into an all-out Bar Brawl.
- The pie fight scene in develops this way; people walk in to the bakery, see what's going on, get hit by a missile intended for someone else and join the scrum—except, of course, for The Great Leslie, who walks through the crossfire unscathed until someone gets him in the face at close quarters. Obviously, this is Played for Laughs.
- Blazing Saddles has a famous one that (literally) crashes through the (in-universe) Fourth Wall, starting out as a street battle pitting the townspeople against the Mooks hired by a crooked railroad tycoon to terrorize Rock Ridge. The combatants eventually brawl their way onto a movie soundstage, where one of them punches the director in the gut and all the castmembers join the fight in retaliation. Then the fight spills over into the studio commissary (packed with extras dressed in various ridiculous costumes, of course), and everyone begins throwing pies at each other.
- One of the several openings of Soap shows a brawl that starts with Burt trying to get in front of Chester for the family photo, but ends up involving all except the Major (who is too out of it to notice) and Billy (who considers himself the Only Sane Man in his family, and sits watching amused by it all) and Benson, the resident Servile Snarker just leans against a wall with a bored look on his face.
- Played for Laughs in The Young Ones episode "Sick", where a misunderstanding between two men outside the Young Ones' house escalates into a full-blown street riot that even manages to draw in the episode's guest band Madness.
- In the M*A*S*H episode "A Night at Rosie's", a dispute over a crap game turns an all-night party into a melee of violence that encompasses the entire bar.
- The parody song "Alla Fiera Thunder Bluff" (based on World of Warcraft), a gnome wizard tries to buy a trinket in Thunder Bluff but is mugged by a Tauren. The following, escalating conflict ends up in a titanic brawl and eventually a Blizzard GM appears, scolds the gnome for causing the mess and then gets fired.
- Happens near the end of the second act of Richard Wagner's Die Meistersinger.
- The opening scene of Romeo and Juliet has a servant of the Capulets taunt a servant of the Montagues with an obscene hand gesture on a street in Verona. This is enough to trigger a gigantic brawl between everyone in both families that soon spreads all over town, until Prince Escalus threatens to have anyone who fights from that point forward executed.
- In Uncharted 3: Drake's Deception, Sully and Nate are jumped in a backroom transaction gone wrong. They fight their way out of the backroom only to be attacked by the patrons in the main room of the bar as well. Nate fights his way through the bar, behind the bar counter, into the bathroom, out of the bathroom, and ends up in the back alley of the bar. The closer he gets to escape, the stronger and more plentiful the mooks.
- The fluff from the aptly-named "Furball" OXP for Oolite:
"You know how it is ... you're sitting at the bar enjoying an icy cold lethal lager when the lobstoid next to you spills his mug of fuming nitric acid in your lap. You jump back, and knock over the blue frog who's been standing behind you chatting up a lady frog. Before you can sneeze, fists and paws and claws are flying, the brawl spills out into the docking bays, and people are threatening to launch and settle it with lasers. Then the cops show up and suddenly most of the merrymakers realize they should really be somewhere else, so the festivities move out the docking bay to the front of the station."
- In The Order of the Stick, the argument between Roy, Gannji and Enor ends up in a gigantic pub brawl.
- Any Flame War almost by definition, especially once it reaches Internet Backdraft levels. True, a Flame War can stay contained between two combatants, but it rarely, if ever, does and almost always instead drags in anyone who sees it — which is why they tend to be so destructive to anywhere they start.
- Subverted in Avatar: The Last Airbender, where Hakoda tries to invoke a prison riot by shoving the stereotypical huge tattooed guy... who responds with words because he's working on controlling his anger. And then double subverted by Chit Sang, who picks up a prisoner and throws him at another prisoner. Yup, that'll do it. (Granted, it's hard to escalate from that point, but it spreads.)
- My Little Pony: Friendship Is Magic: Season 2, Episode 3: "Lesson Zero": Twilight puts a "Want It, Need It" spell on a ratty old toy of hers named Miss Smartypants to get the Cutie Mark Crusaders to fight over it. But because Twilight's in the middle of a freak out, the spell is so strong that anypony who sees the toy wants it and gets into the fight. By the end of the episode, there's a Big Ball of Violence involving everyone in Ponyville except the core cast.
- In the Regular Show episode "Karaoke Video", Mordecai and Rigby's fight over an embarrassing video tape with a karaoke bar's owners escalate into a huge brawl involving all of the bar's guests.
- The Simpsons can't get enough of this trope. The people of Springfield just can't help getting into fights over everything, usually starting with one character becoming so offended by what another character said that he punches him in the face; somehow, this encourages every single person on the street to start brawling with whichever person is closest to them at the time (which backfired horribly on Moe the Bartender once when the person next to him turned out to be a heavyweight champion boxer).
- The Venture Bros. has invoked these a few times.
- In "Tag Sale, You're It", The Monarch started one with a high-speed pebble. It was easy, since Dr. Venture's yard sale had attracted a huge number of costumed villains. Maybe overkill, though, since all he wanted was to sneak inside to use the bathroom.
- In "Now Museum—Now You Don't", the critical mass of heroes and villains is due to the grand opening of a museum honoring the late Jonas Venture. Telepathic villain Brainulo adds the powder by stirring up the guests' fears and shames. Then the abused event staff, formerly a pirate crew, light the fuse by confronting the owner.
Dr. Venture: This is going to be one of those "things", isn't it? I mean, you get a bunch of short-fused, costumed idiots together in one room like this, and what do you think's gonna happen? Any minute now, stuff's gonna start blowing up, guys'll be throwing each other into other guys.
Bodyguard Brock: Yeah, probably.
Dr. Venture: Huh. You know, when you're not the one in the middle of it all for once, it's actually totally, completely obvious.
Brock: Uh-huh. Welcome to my life.
- Many urban riots and similar outbreaks of civil unrest begin this way, with members of one social group bullying around members of another social group. Word begins to spread, and before long there's escalating retaliation on everyone's part.
- The Boston Massacre apparently began this way, with a boy hurling snowballs at a British soldier and getting shoved over for his trouble. Then more colonial protesters started to show up...
- The trope applies on a grand scale to a number of multi-belligerent wars throughout history, but World War I probably exemplifies it the best. A handful of Serbian nationalists throw a lethal punch at one Austrian noble. Austria-Hungary beats up Serbia. Russia says, "Pick on someone your own size." Germany taps on Russia's shoulder, but then swings a fist at France. And Britain charges in with, "See here!" but is knocked over and can't stand back up for four years.