Broken Streak

A run of consecutive losses by (say) the team the main character is on, or of consecutive wins by the team's rivals, or both, comes to an end.

Exceptions are when Failure Is the Only Option, or your would-be streak breakers get diabolically unlucky...or stupid. In other words, if the opposition wins, it's by luck rather than skill.

Anime and Manga

 * Pokémon's Ash Ketchum (or rather, Satoshi) He enters a far worse one after losing a six-on-six battle with Paul. The only battles he's won are the plot-important ones, gym battles.
 * In a Halloween Episode of Axis Powers Hetalia, America (whose only fear is the supernatural), finally defeats the occultist England after 87 losses in their competition of seeing who scares the other first.
 * It should however be noticed that it was probably only because he enlisted Japan's help.
 * In Initial D, Takumi breaks the winning streak of Ryosuke Takahashi, who had previously been considered the best street racer around. In Second Stage, another opponent appears who had wanted that honour for himself.
 * This is in the backstory of Girls und Panzer - Miho's actions that broke her school's winning streak caused her to be treated poorly by at least one of her teammates, forcing her to change schools.

Literature

 * In Harry Potter and the Philosopher's Stone, the protagonists break Slytherin House's seven-year winning streak in the House Cup. Dumbledore gives the Three Amigos enough last-minute points to put Gryffindor in joint first place, and then awards Neville "Why is it always me?" Longbottom another ten for being brave enough to stand up to his friends (the same ones who taught him to stand up to people in the first place) when he thought they were making trouble.
 * A more personal version in Order of the Phoenix: Gryffindor has limped its way to the Quidditch Cup final despite Umbridge kicking Harry and the Weasley twins off the team and Ron's year-long Performance Anxiety issues, but no-one's feeling very optimistic. When Hagrid asks Harry and Hermione to meet him in the forest during the match, they do so. When they hear what sounds like the Slytherins' 'Weasley is our King' song on their way back, they assume Gryffindor lost. Then they notice that the actual lyrics have changed a bit, and see Ron being carried across the field by his teammates...

Live-Action TV

 * 3rd Rock from the Sun: French Stewart makes an impromptu overhaul of a university football coach's strategy during their homecoming game...and then the team goes on to take the win.
 * Dawson's Creek: Also involving football.
 * Usually the protagonist is trying to break the streak. In the case of a Boy Meets World episode, Cory is trying to sustain Mr. Feeny's streak at a geography competition (the resident egghead is uninterested since they're not giving out the usual prizes this year). In the end, Feeny's streak is broken, while the winner spazzes out upon finding out she's getting a different prize from the norm. However, Feeny decides to pin up Cory's A on a geography test where his previous wins had gone.
 * Father Ted - where failure (to get off the island) is the only option - was done in such a spectacular fashion that the priests were about to be kicked off the island by Bishop Brennan, so they would no longer be his problem. Therefore a success was required to maintain the status quo.
 * Subverted in Only Fools and Horses. In one episode, Del constantly says to Rodney that the reason he keeps losing money to Boycie at poker is because he is on a "losing streak" which he feels is about to come to an end. Its actually because Boycie cheats. Del does end up winning a lot of money off of Boycie, but the reason he does so is by cheating better.
 * iCarly: iWas A Pageant Girl had Sam breaking the streak of the long-running champ of a beauty contest. Even though she completely screwed up everything but the final dance routine.
 * Cheers's yearly pranks with rival Gary's Olde Tyme Tavern.

Newspaper Comics

 * The losing streak of Charlie Brown's softball team is legendary. Most of the times they start winning have been when he wasn't able to play for some reason, with the winning streak ending the moment he returned. One exception to that general rule was a winning streak caused by a bug going around that affected every team in the local league except Charlie Brown's, which ended the moment the other players recovered.

Pro Wrestling

 * WCW: Bill Goldberg's 173-win streak (the longest in the history of pro wrestling) finally ended when he got tasered behind the Easily-Distracted Referee's back.
 * The losses he suffered before the streak storyline begun were Retconned.
 * The Undertaker has appeared at Wrestlemania twenty times. After about the tenth time, everyone started making a big deal about who will be the first to beat him. Just ask the guy who did just that.

Video Games

 * Phoenix Wright has broken the winning streaks of Miles Edgeworth, Manfred Von Karma and Franziska Von Karma, while his mentor Mia broke the winning streak of Winston Payne.
 * And depending on what ending you get in the last case of Justice for All

Western Animation

 * Hey Arnold!, "Road Trip": Helga's mom needs $500 to repair her car. Enters bull-riding contest with $500 prize. Rival has won 5 years running. Turns out she was state bull-riding champion, and she takes the money.
 * "Tour De Pond": Not only is it a case of a Family Rivalry, but Rex Smythe-Higgins the 3rd has also won this race a couple years running.
 * In the Peanuts movie Bon Voyage, Charlie Brown, the title character, as he is leaving for France, tells Schroeder to take care of the baseball field, whereby Sally bluntly tells him that "the last time you went away, our team won three games in a row."
 * The only time Charlie Brown's baseball team had a winning streak where Charlie Brown himself wasn't benched for some reason, it was because a bug was going around that made all the other teams too sick to play. Said streaks invariably ended when Charlie Brown returned to the game or the other teams recovered.

Real Life

 * The Boston Red Sox in 2004.
 * And the White Sox the year after.
 * January 5, 1971: the Washington Generals beat the Harlem Globetrotters 100-99, bringing the Globetrotters' winning streak to an end at 2,495.
 * After 11 films from Pixar, all certified fresh on Rotten Tomatoes, they released Cars 2, which is currently at 38% on the Tomato-meter. Also, all Pixar films released since the establishment of the Academy Award for Best Animated Feature in 2001 has been nominated for it, except Cars 2.
 * Predating Cars 2, Toy Story's streak of 100% Rotten Tomatoes ratings ended when Toy Story 3 got...99%.
 * Susan Lucci's run of Daytime Emmy losses for Erica Kane ended in 1999. This 28-year streak included 21 nominations.

Live-Action Television

 * A Minute With Stan Hooper: The titular newsman wants change in the town he's moved to (it doesn't even allow women to vote), and decides to run for mayor against the 20-year incumbent, a bait shop owner who happens to have a political aide backing him. After spending a better part of the ep drumming up support, he ends up getting just 2 votes: himself...and the mayor's aide.
 * Gilmore Girls, "They Shoot Gilmores, Don't They?". Lorelei is desperate to break Kirk's winning streak (and her own streak of futility) at a dance marathon and almost does it (just like last year), but her partner / daughter Rory runs off the floor with fifteen minutes to go after breaking up with her boyfriend Dean (the real important event in this eppy), leaving Lorelai with yet another 23rd-hour loss as Kirk outdances the others to win his 5th in a row.

Western Animation

 * The telefilm The Jetsons Meet The Flintstones: Looks as if Nate Slate is about to end his losing streak to a rival in a pig catching contest...time for Dino and Astro come in and inadvertently help sustain the rival's streak.
 * South Park, "Big Gay Al's Big Gay Boat Ride": QB Stan is looking for his gay dog Sparky, while his football team continues its decades-long losing streak against Middle Park without him. Fortunately, the denizens of South Park were more interested in beating the 60-point spread, and Stan shows up in time to at least do that.
 * As Told by Ginger, "Next Question": Ginger's school Lucky Jr. High up against 9-time winner Furnace Brook in a televised quiz contest. Ginger asks her quiz team coach out on a date (!) right on the air (!!), resulting in Furnace Brook continuing their streak.

Theater

 * Used absolutely chillingly in Rosencrantz and Guildenstern Are Dead, when Rosencrantz spends the first ten minutes of the play desperately trying to break a streak of turning up heads every single time he flips a coin. He can't. It's their first clue that reality is warping, and that they're stuck in something powerful that they might not be able to escape from by following any of the usual rules.

Real Life

 * The Boston Red Sox...in 1986. Bottom of the 10th, two outs, Sox lead 5-3. Then: single, single, single for a run, pitcher switch, wild pitch for the tying run, grounder through Bill Buckner's legs for the win.
 * The Chicago Cubs in 2003. Almost made it to the World Series, which they haven't been to since 1945, but despite having their best pitcher on the mound and holding the lead twice, they still lost Game 7 of the NLCS.