Escalating Brawl

The heroes entered the classical old pub. A particularly nasty guy taunts one of the characters and tries to hit him. The hero dodge and the other guy hits a bigger, nastier guy who proceed 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, launching 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.

See also Bar Brawl, Food Fight, Diner Brawl and Everyone Join the Party. Don't confuse with Escalating War.

Anime and Manga

 * In Fairy Tail, the first time we see the titular guild, Natsu causes one of these. Luckily Makarov stops the brawl before they resorts to magic.

Comics

 * Happens several times in Tex Willer, including an epic brawl that ended when the resident Boisterous Bruiser Gros Jean kicked all the bad guys out of the inn and then chopped the supporting pillars with an axe, wrecking the whole place.

Fanfic

 * 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.

Film

 * 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.

Live Action TV

 * 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).
 * 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.

Music

 * 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.

Theatre

 * Happens near the end of the second act of Richard Wagner's Die Meistersinger.

Web Comics

 * In Order of the Stick, the argument between Roy, Gannji and Enor ends up in a gigantic pub brawl.

Western Animation

 * My Little Pony Friendship Is Magic: Season 2, Episode 3: "Lesson Zero": Twilight puts a love spell on a ratty old toy to get the.
 * 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.

New Media

 * 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.