Accidental Athlete

Someone (usually a child or teenager) is discovered to have a natural athletic ability while doing something else. They usually assume they are in trouble when they are spotted and called out for it. Common examples include showing off how quickly they can run away (in a high school setting, expect it to be the class nerd becoming a good sprinter by being forced to outrun the school bullies.) They'll quickly be recruited to save the local team from failure, becoming an Accidental Athlete.

Anime and Manga

 * Sena in Eyeshield 21 is picked up as a runningback for the Deimon Devil Bats after Hiruma sees his running and dodging skills as Sena runs from the Ha-Ha Brothers.
 * Also Karin, who apparently developed a gentle, yet powerful throwing technique just by practicing piano and drawing manga.
 * The Ha-Ha Brothers were initially blackmailed into linemen before they discovered their love for the game.
 * Unbelievably, Shin. He had no intention of playing any sports and only tried out for the White Knights because Sakuraba asked him to.
 * Averted in Sayonara, Zetsubou-sensei where Fujiyoshi is asked to join a baseball team after hitting a home run, but says she's only there to do research for a manga.
 * The school athletic clubs are also trying to drag her to join, because despite the Nerd Glasses, Harumi is a very competent athlete. She just has better things to do.
 * In one Filler episode of Tokyo Mew Mew, Ichigo's secondary abilities from being a Catgirl, such as jumping high and landing on her feet, get her dragged onto the gymnastics team. Fan Service ensues when the recruiter forces her into a leotard.
 * In Samurai Champloo, Mugen is drafted into playing baseball against the Eagle Land navy team after the Japanese organizer sees how fast he can run from the restaurant he failed to pay at, in addition to the fact that he can throw a baseball hard enough to knock down a wooden tower about a mile away.
 * Hajime no Ippo - After a timely rescue from bullies (well, maybe not that timely) by passing jogger Takamura, Ippo gets an impromptu Boxing Lesson just for fun: punch bag, feel better. Instead, he punches the bag nearly to the ceiling and splits all the skin on his knuckles. Turns out spending a childhood or two moving heavy fishing equipment will build muscle like nobody's business.
 * While the more common "running away skills" come into play, it's not until after he actually starts training.
 * In One Outs, Kojima discovers Tokuchi largely by chance.
 * In the My Heavenly Hockey Club manga (which is a slightly more sadistic and straight-forward version of Ouran High School Host Club), Hana is recruited because she was struck by a car and survived... and is more or less invincible in her sleep.
 * This is how Kasuka Heiwajima got his start as a Teen Idol in Durarara!!—Originally, the talent scout was interested in recruiting his (ludicrously volatile and super strong) brother, Shizuo. Kasuka saved the poor guy from the resulting beatdown and was scouted in Shizuo's place.
 * Somewhat averted by Haruhi Suzumiya. She joins every club in the school proving herself to have incredible talent in athletics along with just about everything else. However, she refuses to stay in any of those clubs because they don't hold her interest.
 * Digimon Xros Wars has Taiki who has join many clubs in general, and in each of them he's able to pull them off like a pro.
 * Hanamichi Sakuragi of Slam Dunk, although he wasn't doing something else except blow off his top at hearing the word "Basketball". Haruko only notices his height and his build which is perfect for the sport. Skills-wise, though, he cannot play to save his life.
 * But he is a fast learner. Coach Anzai saw it too, and had Sakuragi master the basics. In no time, he became Shohoku High's starting power forward, slowly working his skills to become the team's rebounder and center under the basket when Akagi isn't around.
 * Played for laughs in Katteni Kaizo. Chitan is actually a god of soccer, and had he pursued this talent he could have rocked the planet, but he's only interest in trains, and his potential is wasted.

Comic Books

 * In "The Greatest Pitcher in the World!" in Superman #77, an amnesiac Superman, who is living as a hobo, is recruited as a baseball pitcher after he returns a fly ball and almost breaks the catcher's hand.
 * In Marvel Adventures Spider-Man #34, Peter Parker is recruited as a shortshop for his high school baseball team after he's seen using his super-powers to deftly catch and return a wayward ball. Team pitcher Flash Thomson is enraged because he suspects Parker's skills are due to illegal drugs, while the Green Goblin wants to eliminate Parker so his son's rival team can win instead.
 * Peter's skills are so accidental he can't mess up his game even when tries to. Peter deduces that his battles with super-villains have honed his reflexes so much that he can't help but react to the ball.

Film

 * In the new St Trinian's movie, Annabelle Fritton is recruited for the hockey team after she smashes a bust with a mobile phone she belted with a hockey stick.
 * Forrest Gump becomes a star running back while being chased through a college football practice field by bullies. It helps that he's seen running by Paul "Bear" Bryant, universally considered to be one of the greatest American football coaches of all time.
 * Forrest Gump again with Ping Pong. "Keep your eye on the ball" indeed.
 * Forrest Gump yet again starts off the national jogging craze while Walking the Earth after tragedy hits his life.
 * Accidental Athlete also occurs in (at least) two Adam Sandler movies:
 * In Happy Gilmore, Happy's ice hockey skills unexpectedly transfer to playing golf, and
 * In The Waterboy, the title character is discovered to have unique tackling abilities.
 * Specifically in the latter, he is a college waterboy who gains incredible adrenaline-based tackling powers when anyone insults his beloved H20 or his beloved momma.
 * In The Blind Side, Michael Oher excels as a linesman only when he learns to tap his "protective instinct." After Oher's foster mother Leigh Anne Tuohy discovers his 98th percentile score on the 'protective instincts' category of an aptitude test, she understands how to extend his custodial nature to the gridiron.
 * Which was some Hollywood History on the film makers part, as Oher was a football player since at least Jr. High.
 * In the first two movies of The Mighty Ducks series, a special-shot hockey player is found and recruited:
 * In The Mighty Ducks, Fulton Reed (who did not play hockey before at all) is recruited after slap-shotting a hockey puck into Gordon Bombay's van that he (well, technically, the driver assigned to him) began using to shuttle all the players around. He has to be taught how to ice skate.
 * The Disney movie The World's Greatest Athlete, who turns out to be a Mighty Whitey Nature Hero.
 * In Rookie of the Year, the twelve-year-old protagonist has his newfound pitching ability discovered when, from about the middle of the stands, he throws back a home run ball hit by the opposition...and hits home plate.
 * He develops his cannon arm after the healing process from a broken arm.
 * The end of Jerry Maguire doesn't make this into a plot point, just into one last joke, when the kid turns out to have a wicked throwing arm when throwing a baseball back to a team that let it get away from them, and Jerry (a sports agent, if you haven't seen the movie) starts musing about training him up...
 * A similar scene happens with a young girl in A League of Their Own, a movie about women's baseball during World War 2, only the girl is black and the team is all white, making an implied statement about who could play pro baseball and who couldn't.
 * Happens in one of The Three Stooges early shorts.
 * Class Act: Duncan Pinderhughes ends up discovering that he has an uncanny ability to kick field goals, and joins the school's football team.
 * Subverted in Sudden Death. At one point, Darren McCord actually has to pretend to be the Pittsburgh Penguins goalie to avoid the terrorists who have invaded the arena. He even makes a save.
 * The Garbage Picking, Field Goal Kicking Philadelphia Phenomenon is a movie about a garbageman who is spotted punting water jugs at the garbage dump and is quickly signed to the Philadelphia Eagles as a kicker.
 * In The Great Gildersleeve, Leroy accidentally hooks up a treadmill backwards and Throckmorton ends up running backwards on it. But he runs so fast that he challenges Judge Hooker to a backwards race.
 * Happens to Sach in a few Bowery Boys movies, usually thanks to some Applied Phlebotinum.

Literature

 * Harry Potter is picked as seeker for the Quidditch team after making a one-handed catch of Neville's Remembrall during his first time on a broomstick.
 * In a fifty-foot dive that a teacher describes as 'even Charlie Weasley couldn't have done it, and he could have played for England'.
 * The 'thinking he's in trouble' aspect of the trope is justified in this case - first years are not premitted to fly brooms and are the only year forbidden from owning one, so diving like that would be a very valid reason for him to be in trouble.
 * First years are allowed to fly, just not allowed their own brooms or to be on the Quidditch team, so flying on the broom was excused, but he was flying without supervision while Madam Hootch took Neville to the hospital wing, so he was breaking that rule.
 * A similar incident to The Simpsons's example below occurs in the Gordon Korman novel The Chicken Doesn't Skate. The school's resident loser, constantly picked on by the Jerk Jocks of the hockey team, turns out to be a brilliant goalie because he has so much practice catching all the toys his toddler brother throws at his beloved computer.
 * Another Gordon Korman example: Rudy Miller from "I Want to Go Home!" At summer camp, he claims that he "doesn't do [insert sport here]" for half the book...until it's revealed that he's insanely good at everything athletic.
 * Discworld:
 * Rincewind may be an utter failure as a wizzard, [sic] but he has become a champion sprinter from all the dangers he's had to run away from.
 * Zig-zagged with Trev Likely in Unseen Academicals: his skill at kicking a tin can around when he's supposed to be working in the University candle vats certainly attracts the attention of their nascent football team, but he insists he promised his mum not to play, although he agrees to help train them. Then when he does join the team, it turns out skill at kicking a can ("You've got the long spin and the short spin") doesn't equate to skill at kicking a round ball. But there turns out to be a way round that as well.
 * P. G. Wodehouse used this sometimes; in The Inimitable Jeeves a fat boy is found to be a remarkable runner after he insults someone and has to run from a beating.
 * In Sword of Truth, Richard gets conscripted into a Ja'La team after he slaughters his way through a considerable number of soldiers in an almost-successful attempt to free himself.
 * To elaborate, it's not his fighting skills or athletics that get noticed so much as his strategy in weaving through a horde of foes towards a goal point; Ja'La being loosely analogous to American football.
 * In Choosing Up Sides, Luke wanders into the outfield of a baseball game, where he picks up a ball and hurls it about three hundred feet to home plate. Having been raised by a fundamentalist preacher whot forbids sports, he's uncomfortable with the attention from everyone who wants him to pitch for the local team.
 * In Infinite Jest, the older brother in the family starts out playing tennis, and is really good at it, but in college, he tries out for the football team, only to find that he isn't big enough. As he is leaving the try-out, he punts a football, and the coach realizes he is a really good kicker.

Live-Action TV

 * "Waikiki Hockey", a Saturday Night Live sketch parodying Elvis Presley movies, featured a busboy who became the starting center for the Waikiki Kings after being spotted clearing the table with a hockey stick-shaped piece of driftwood. It helped that the busboy was played by that Saturday's host, hockey great Wayne Gretzky.
 * Clark Kent in one early Smallville episode.
 * An episode of The Secret World of Alex Mack has one of these, where Alex is sprinting down the hallway of her school attempting to avoid being late to class and getting in trouble. She is still late for class, but instead of getting chastised she is instead recruited for the track team.
 * In Glee, Kurt's dance skills unexpectedly earn him a spot as kicker on the school football team.
 * In Little House On the Prairie, when Pa is getting ready for a baseball game against a team from Sleepy Eye, he and Half-Pint are at Jebediah Mumfort's farm where they both witness Jebediah trying to hit a chicken hawk with a rock. He throws the rock so hard, it puts holes in the side of a barn. After this display, Pa convinces Jebediah to try out for Walnut Grove's baseball team. Of course, he's a natural and helps them win the big game despite all the cheating and poor sportsmanship of those evil people from Sleepy Eye.
 * Even Stevens: In "Head Games", it is discovered that Twitty has incredibly aim when he is enraged at Louis. He joins the baseball team as a pitcher, with a photo of Louis on the catcher's mitt.
 * In Everybody Hates Chris, the titular character is recruited by the basketball coach who sees Chris shooting a wad of a paper into a trash can. Alongside the fact that Chris must be able to play basketball, he has Chris join the team. Subverted when Chris fails horribly at the sport.
 * Josh from Drake and Josh is forced to join the high school football team after his brownies, poisoned by his prankster sister, gets one of the players sick.

Video Games

 * In Phantom of Inferno (game only), Drei is discovered to have natural assassin abilities. Right after the hero pretends she does, no less.

Web Original

 * Cyanide & Happiness, "Waiting for a bus" short. This being Cyanide & Happiness, the trope is Deconstructed.

Western Animation

 * In Kim Possible, Ron Stoppable cheats his way into the quarterback position on the school football team, only to discover his 'mad running away skills' make him a natural running back after his deception is exposed.
 * In the Classic Disney Short Casey Bats Again (a sequel to Casey at the Bat), Casey discovers his daughters form a natural girls' baseball team as they practice their skills while doing the dishes.
 * In The Simpsons episode where Bart and Lisa compete in hockey, her talent as goalkeeper is discovered when Apu sees her block all the paper balls that Bart throws at her while taunting her.
 * In another episode, Bart discovers he is a natural ballet dancer while trying to remove his leotard.
 * Lisa also discovers a natural talent for gymnastics because of her big head.
 * And then, in the most implausible example yet, Homer is discovered to have the toughness necessary to succeed as a professional boxer when he blithely takes a beating from three other fathers who are angry that Bart ratted on their boys. Hell, The Simpsons seems to fall back on this trope often.
 * Homer also makes for a great opera singer while he's horizontal. Also a great painter. Both on the same episode.
 * Lisa discovers in one episode she has a natural talent for ballet when she gets angry at the instructor, who notices her never-before-mentioned "lecturing stance".
 * Rocket Power has Sam Dullard becoming a goalie this way as well. He and Reggie are having a casual conversation while Otto and the gang play street hockey. A wayward slapshot speeds in Sam's direction, and Otto, horrified at what will be an inevitably ugly collision, shouts "LOOK OUT, SAM!" Sam lifts his left hand and coolly deflects the puck WITHOUT EVER TAKING HIS EYES OFF REGGIE. Needless to say, the opportunistic Otto recruits Sam to play goalie for their team, which just happened to be a position they needed filled.
 * As did Mikey in Recess.
 * An episode of Family Guy has Peter running to the bathroom at a high-school reunion, knocking down with ease everyone in their path. Patriots quarterback, Tom Brady, happens to see how well he fights off the people and puts him on the team.
 * In An Extremely Goofy Movie, the antagonists place Goofy on their skateboard team after they notice his expert ability to compensate for his own clumsiness, placing him against his own son Max in a skateboarding championship. Naturally, Max isn't concerned as he notes himself that his dad is the most athletically challenged person in the universe before Goofy quickly proceeds to be really really good (though he had a bit of help) and to the stunned amazement of pretty much everyone there instantly becomes a school hero.
 * Max's comment is extra funny when one remembers that most of Goofy's solo cartoons from back in the day revolved around Goofy's ineptitude at sports.
 * In an episode of Doug while fooling around he accidentally kicks a football over the fieldgoal along with his shoe and is recruited for a position in the school football team. Unfortunately, he can't do the kick a second time.
 * Happens on a regular basis to Candace on Phineas and Ferb.
 * In Rocky and Bullwinkle Wossamotta U story arc, football scouts saw Bullwinkle's throwing ability and give them both college football scholarships to help winning the games.
 * Kung Fu Panda: Po, who was previously thought to be hopelessly clumsy, inadvertently demonstrates his agility when he climbs up some shelves in order to steal some cookies.
 * In the Looney Tunes short Bugged by a Bee, an ongoing war with a bee accidentally causes Cool Cat to be become a champion pole vaulter, baseballer, rower, hurdler and footballer at college. Parodied at the end, where Cool Cat is congratulated on his contributions to the university's athletic success, and a trophy is awarded to "the one who made it all possible... the bee!"

Real Life

 * Football great Jerry Rice was recruited for his high school football team after he ran away from the principal who caught him playing hooky.
 * Jim Thorpe, winner of several Olympic Gold medals, got a spot on his school's track team when he beat the high jumpers while wearing street clothes.
 * In 2008 The Greece (NY) Athena High School basketball team realized that Jason McElwain, their autistic long-time team manager, was about to graduate. So they decided to say 'thank you' at the last home game by letting him play after they were safely ahead during the fourth quarter. He promptly scored 20 points, and I bet they were left wishing they'd put him in a lot earlier... like during his freshman year, perhaps.
 * As a child, Boxing icon Muhammad Ali was offered his first boxing lesson by the police officer to whom he'd reported his stolen bicycle. He only took up lessons so that one day he'd be able to beat up the kid that stole his bike...the rest is sporting history.
 * Not exactly "unrelated activity", but California/Anaheim Angels closer Troy Percival started out as a catcher until the coaches discovered that his returns to the mound were often faster than the other pitchers.
 * Similar to Percival, Kenley Jansen was a Dutch catcher in the Dodgers minor league system who came to attention when he threw out two runners in a row during the world baseball classic. He's currently a relief pitcher on the main roster.
 * Likewise, because it's less strenuous on the arm than most other pitches, position players sometimes fool around with throwing the knuckleball in their spare time. Tim Wakefield was a poor-hitting minor league first baseman when he was discovered to have a talent for throwing the knuckleball and has been a moderately successful pitcher at the major league level for almost two decades.
 * The reverse of this is Babe Ruth's story: As a pretty good Boston pitcher at the time, he was converted to the outfield when his propensity for good hitting and gargantuan home runs revealed itself. He would still pitch, but not nearly as often, until he was traded to the Yankees and became a pure outfielder.