Not Just a Tournament

This can be any sort of plot where an organized competition isn't a simple Tournament Arc, but rather has a behind-the-scenes plot going on. Sometimes the tournament starts out by looking like a mere framing device for the story, then is shown to have a sinister behind-the-scenes purpose. Other times the behind-the-scenes plotting is used as The Reveal. Most of the time, this trope is used as either a setup for a Summation Gathering or the Big Bad's climactic attack on the hero. If there isn't some deeper hidden purpose to the tournament (and there really is just a Framing Device at work) then this isn't the trope you're talking about.

Regardless of the exact type of tournament this often results in whatever reward was promised to the winners being a ruse. At the worst the tournament is Unwinnable By Design. Sometimes its sinister purpose is derived from perpetuating the competition.

Since this is often presented as The Reveal, spoilers ahoy!

Anime and Manga

 * Naruto's Chunin Exam arc features a single-elimination tournament as the final stage of the exam. Initially, the idea is that the contestants will fight each other and that the judges determine who should be promoted based on the performance. However, it is soon explained that that function is more of an in-universe Excuse Plot to showcase competition between villages. Said competition affects incoming business for each village.
 * Revolutionary Girl Utena: The winner of the Rose Duelists' tournaments will hand over the godlike power of Dios to Akio, then be promptly disposed of.
 * Shitsurakuen: Whoever collects all six seals in Exaclan will... actually, never mind, the ending is too confusing to tell, but it's certainly not about rounding up a six-girl harem.
 * Master of Martial Hearts is a big time (and convoluted as hell) case of this. The tournament revolves around the "Platonic Heart," a mythical jewel that can supposedly grant any wish to a girl who acquires it. Every girl who loses the tournament is Mind Raped into an Empty Shell state before being conditioned into sexual slavery and sold. The entire thing is being conducted as a Cycle of Revenge by the daughters of two sisters who wound up on the losing end of a similar tournament organized by Aya's father, which Aya's mother won. The two cousins want the same thing their mothers got put through to happen to Aya as revenge against both of her parents, and they don't care about what happens to the other contestants.
 * Mahou Sensei Negima had a tournament whose hidden purpose was to gather evidence of the existence of magic and flood the media with it.
 * Virtually every Tournament Arc in Yu-Gi-Oh to the point where a filler arc has a character comment in-story how refreshing it is to go to a tournament that's only a tournament (it still manages to get hijacked by a villain's scheme, but at least that wasn't in the host's plans).
 * Yu Yu Hakusho: The Dark Tournament ark is already pretty, well, Dark, but then it is revealed that the true purpose is for betting and power brokering behind the scenes. The later Demon World Tournament is a complete aversion of this trope, especially considering where it takes place.
 * The "D of D Tournament" in Kenichi the Mightiest Disciple, where both the bad guys (who organized the event) and the good guys are engaged in various activities behind the scenes which are as important as the tournament itself. The climax of these background activities takes place simultaneously with the final tournament battle between Kenichi and Kanou.
 * G Gundam has the Gundam Fight, which occurs regularly every four years. However, in the 13th Fight we have the Devil Gundam getting loose and trying to destroy the planet, while several nations vie to find and take control of it for their own purposes.

Eastern European Animation

 * The Adventures of Captain Vrungel cartoon is about an international regatta with the purpose of smuggling out a stolen sculpture.

Film

 * In The Quick and The Dead, the gunfighting tournament is primarily a way for the Big Bad to eliminate any threats to himself and intimidate any of the locals who might try to oppose him. He knows that there is an assassin gunning for him and that the Kid is itching to take him on. The tournament is a trap for them to face him in the open where he can gun them down in a duel. It is implied that if anyone proves too much of a threat, his Mooks will gun that person down.
 * In Enter the Dragon, the hero participates in the tournament, but was actually sent there to uncover the evidence about the tournament organizer's criminal activities.
 * In the Dead or Alive film, the villain's tournaments are used to collect fighting information to create sunglasses that turn the wearer into a master martial artist.

Literature

 * The Odyssey: When Odysseus returns to Ithica, he orchestrates an archery competition for the suitors that have been vying for his wife's hand while he was away. Odysseus wins the tournament, being the only man strong enough to string his old bow in the first place, to prove his identity. He and his son then proceed to massacre all the suitors who showed up for the tournament.
 * Knights Of The Forty Islands: The team that first comes to control all 40 eponymous islands will be sent back home... NOT. Actually, the game is rigged so that no team can ever achieve victory, and the kids can never ever go home again.
 * Fred Saberhagen's Berserker novel Berserker's Planet. A cult on Hunter's Planet regularly has tournaments where the contestants fight to the death. Little do the competitors know that the ultimate controller of the cult is a disabled Berserker which is doing its best to carry out its programming to destroy all life.
 * Doubly subverted in Harry Potter. Everyone thinks its a ruse to kill Harry during the contest. In truth, it is rigged for him to win, so he can be captured at the moment of victory. Note that the Tri-Wizard Tournament isn't evil by design, just hijacked by the villains in that particular instance.
 * Deltora Quest - Book IV: The Shifting Sands. Leif, Barda and Jasmine enter in a tournament for money to continue their travels. The problem is, the tournament is a trap. After Jasmine wins, they are kidnapped by the evil Shadow Guards as a method of keeping the population quiet IIRC.
 * "The Mystery Knight", one of the "Dunk and Egg" prequel stories to A Song of Ice and Fire, takes place during a tournament that's.
 * Also, supposedly the infamous Tournament at Harrenhal was reported to be one of these. The only reason King Aerys, who had not left his castle for some years, attended, was because he had been told that his son Rhaegar was gathering the nobles of the realm to plan for a coup. This story has not yet been confirmed.

Live Action TV

 * This happened a few times on Tales From the Crypt, where a contestant in a contest murders the odds-on favorite, but finds out too late that the "prize" for winning is death. In one case, an actor literally kills for a chance to play Hamlet, but discovers that he was really auditioning to play Yorick [the skull]. In another case, a Beauty Pageant contestant kills another, but discovers that the pageant is "Miss Autopsy".
 * In the Leverage episode "The Queen's Gambit Job", the heroes set up -- and then rig -- a blitz chess tournament as a way of distracting the mark of the week during a theft.

Oral Tradition

 * The archery tournament in the various versions of Robin Hood. It's simply a ruse for the bad guys to flush out Robin, knowing full well that he would not resist entering the tournament and winning it, especially if the prize is a kiss from Maid Marian.

Tabletop Games

 * Champions campaign The Great Supervillain Contest. The Crimson Claw sets up a competition among the Earth's greatest supervillains to determine which one is the most powerful. The prize is the Emerald Eye of Azog, which will increase the winning villain's already great abilities. What the villains don't know is that once the winner bonds with the Eye, it will take him over and turn him into a gate that will allow dangerous demons to come to Earth.

Video Games

 * The plot for Mega Man 6 involves a certain Mr. X, who is totally not a disguised Dr. Wily, organising a fighting tournament for robots with prizes for the laboratories developing them; Mega Man has to stop the eight finalist robots of the contest after Mr. X reprograms them to Take Over the World in his stead.
 * This is pretty much The King of Fighters in a nutshell, most prominently during The Orochi Saga (95-97) and The Tales of Ash (2003-XIII), where the primary motive of the baddies is to unseal Orochi (although for varying, but no less equally evil purposes). This has happened so frequently that characters start lampshading why there can't be a regular fighting tournament that doesn't serve as the instrument for The End of the World As We Know It every once in a while.
 * Bloody Roar can be best described as X Men meets the King of Fighters. Each tournament revolves around diplomatic tensions between zoanthropes and humankind due to experiments being conducted on zoanthropes, behind the scenes. The tournament itself is merely a front to lure the strongest of their kind to be test subjects, by pitting them against others of their kind with legendary beast power... or genetically enhanced super beings.
 * In Street Fighter II, Bison's holding a tournament to get revenge on the characters who ruined his plans in Alpha 3. In Street Fighter IV, Seth from S.I.N. (Shadaloo Intimidation Network, the weapons division of Shadaloo) holds a tournament to gain data (and Ryu) to complete his BLECE Project, an unknown bioweapon. The tournament in Street Fighter III: New Generation/2nd Impact subverts this, though. The Illuminati is judging people the world wide to see who is fit to live in the new utopian world foretold in their ominous prophecy, but their leader Gill is a Well-Intentioned Extremist.
 * Tekken 2: Kazuya announces the King of the Iron Fist Tournament 2 to get rid of Heihachi and his other enemies. Tekken 3: Heihachi announces the King of the Iron Fist Tournament 3 to lure Ogre out in order to capture him using the contestants as bait. Tekken 4: Heihachi needs to get the devil gene to become immortal so he announces the King of the Iron Fist Tournament 4 to lure Kazuya and Jin out to obtain the devil gene.

Western Animation

 * Teen Titans episode "Winner Take All". A number of teen superbeings are teleported to an unknown location, where the Master of Games invites them to take part in a Tournament of Heroes that will determine which of them is the greatest young hero on Earth. What the competitors don't know is that when they lose, they're trapped within the Master's jewel so he can use their powers.
 * The World Grand Prix from Cars 2 was actually organized by the Lemons just so they can zap all of the competing racecars with a deadly radiation cannon as an attempt to destroy all alternative energy sources and force everyone back to using gasoline.