In Terminator 2: Judgment Day, John Connor makes the T-800 swear that he won't kill anyone. Programmed to obey John Connor, the T-800 agrees, and promptly follows it up by shooting out a security guard's ankles, since John only ordered him to not kill anyone.
T-800: He'll live.
In the film adaptation of Dick King Smith's Babe, Farmer Hogget plans to enter Babe in a herding contest for dogs... despite Babe being a pig with an odd talent for sheepherding. He was concerned that the entry papers might say Name of Dog, because he couldn’t in good conscience put "Pig" down for that. The form, however, says Name of Entry. So Farmer Hogget is in the clear: it never asked you to specify that you were entering a dog.
This was in the book too, with the added comment of people possibly remarking "Pig? That's a funny name." without realizing it was the honest truth.
Batman Returns: The Penguin assures Catwoman that he will scare the Ice Princess when they kidnap her. But notice that he didn't say scare her but not kill her.
"She looked pretty scared to me!"
In RoboCop (1987), the villain Jones secretly programs a fourth directive into Robocop that prevents him from harming Omni Consumer Products personnel, which keeps Robocop from arresting him after revealing his involvement in the death of rival colleague. Later, Robocop goes to a board meeting where Jones is, not to kill him because of the fourth directive, but to show damning footage of his wrongdoing. Conveniently Jones had earlier told Robocop what exactly the classified fourth directive contains, and nothing in his programming is preventing him from spreading this information further. When Jones tries to take the CEO hostage, the CEO fires him. Since Jones was no longer employed at OCP, that meant the fourth directive no longer applied to him, which meant Robocop could finally give him his comeuppance.
Cain in RoboCop 2 uses the same tactic on a subordinate who failed him. When his mistress protests that he said that he would only scare the guy while he's having him cut open with surgical tools, Cain flatly states "Doesn't he look scared?"
Barbossa uses and subverts this. Like all good ruleslawyers, Barbossa has no problem with the rules bending—as long as they bend in his favor.
Barbossa: First of all, returning you to Port Royal was never part of our negotiations or agreement, so I must do nothing. And secondly, you have to be a pirate for the Pirate Code to apply, and you're not. And thirdly - the Code is more what you'd call "guidelines" than actual rules.
Plus, his agreement to release Jack and Elizabeth... with no specification about when or where, so he just maroons them on an island. They're lucky he didn't "release them" to the sharks.
In Star Trek II: The Wrath of Khan and the 2009 Star Trek film, the Kobayashi Maru test. Starfleet actually had to add a "no reprogramming the simulator" rule after Kirk's shot at it, and according to the Expanded Universe, this kicked off a whole tradition of loopholing the scenario.
Not only that, but it became an expectation of any student to find a way to beat the simulation with outside-the-box thinking.
In the opening to Star Trek Into Darkness, Spock cops to Kirk and Bones violating the Prime Directive by rescuing him in broad daylight before a primitive alien species, yet still argues the point that they wouldn't have been violating the wording of the Prime Directive had they not been detected. Because then the natives would never have known that the Enterprise crew had interfered with their development by saving them from extinction. Admiral Pike doesn't buy it, feeling the spirit of the law was more important, and Kirk ends up getting demoted off the captain's chair....temporarily, only to get it back to pursue Khan after Pike is killed.
In the Swedish movie The Call-up, the protagonists (who are doing their military service) are out on exercise and need to drive back to base. The quickest way back is over a bridge, but the bridge has been declared destroyed (and everyone is supposed to play along) and a guard refuses to let them pass. Their solution? They drive to a hardware store, buy some paint, and paint the words "Helicopter" on the truck. The guard can't stop them crossing that way.
In The Dirty Dozen the named dozen are in war games when they switch their armbands to the other side's color and infiltrate their headquarters. When questioned on this tactic, they reply, "We're traitors".
In Air Bud, there is apparently no rule against a dog playing basketball. Probably because no one ever thought that would come up ever.
Combination of Truth in Television and artistic license. You would be hard-pressed to find a "the players have to be humans" rule. However, most schools have rules preventing pets from being taken onto the premises and rules governing the handling of live animal mascots. Bud would never have been allowed on the court, except perhaps for a half time stunt.
In the movie Winning London, the Olsen twins have to save some "hostages" as part of a Model UN convention/competition. As it's all pretend, the hostages are just in the next room over, so they take the literal approach and climb through the air vents to save them. After coming back into the room, one boy shouts "You said we had to work it out on paper!", to which the official responds "No, I said you had to work it out."
Flubber where the professor put flubber on the shoes of his school's basketball team when they are losing an important game. As a result, the team suddenly find themselves able to easily make impossibly high jumps to win the game. Although the coach of the opposing team protests this development, the stunned referee refuses to stop play because there is no rule that establishes a height limit of players' jumps, even though it is obvious this sudden advantage for the team appearing mid-game must be be the result of some kind of external aid that is likely against the rules.
Semi-Pro: Ain't no rule says you can't play drunk. Well, there is a rule, but they can't enforce it. ("Remember those 30 free throws I did in Minnesota last year?" "Yeah?" "I don't.")
Also, when they first use the alley-oop, the ref rules it a violation, although the protagonists are ready and throw the rule book at him. The ref is forced to allow it.
In the movie Blades of Glory there ain't no rule saying two guys can't skate as a pairs team. note In Real Life, there is for Pairs Skating in the Winter Olympics (spoil-sports), but the competition in the movie is the fictional "World Winter Sports Game".
In Zoom, in the final scenes of the movie as we see the 'Happy-Ever-After' scenes for each of the super-powered kids, we watch the expanding boy playing soccer as the goalie and being the team hero, as there Ain't No Rule against being able to expand your body parts to block the entire goal so no shots can go in.
Shows up in the ending to Juwanna Mann, where a male basketball player is forced to play for a WNBA team, crossdressed, and wins the final game for them. He wins by making a slam dunk, which IS forbidden in WNBA rules. In fact, it was brought up earlier in the movie that he could NOT score using slam dunks. Which is a departure from real WNBA rules, which do not prohibit dunks. It's just that very few women can dunk on a 10-foot rim.
Necessary Roughness and Waterboy. Ain't no rule that a man can't play football among boys! In Necessary Roughness, the rule is the NCAA eligibility rule, which states that a player begins his eligibility the day he first enrolls in college. So technically, though Blake was 34 years old, he's a "freshman" to the NCAA; he has three full years of eligibility remaining after the movie. A notable real-life example is Chris Weinke, who played six years of minor league baseball (for which he would not have been eligible to compete at the NCAA level) before enrolling ad Florida State and becoming a quarterback in football (for which he still was eligible.)
Also no rule against women playing in Roughness, as Lucy, a women's soccer player, joins the team. It's even lampshaded by Robert Loggia's character. This is true to life as well; there have been a handful of female kickers at the college level in real life.
In D2: The Mighty Ducks, the Ducks try on new uniforms (which were the uniforms of the just-created Anaheim Ducks, which in the timeline of the films were not yet invented) for the third period of the final game (they before had been Team USA). Despite the opposing coach's protests, the play-by-play announcer notes that he has "just been informed that there is no rule against changing uniforms during a game".
In many sports there actually isn't a rule about changing uniforms halfway through. Some teams raise money for charity by doing this and then auctioning off one set of uniforms after the game. Usually, though, they're duplicates of the same uniform, and teams generally don't wear different uniform designs during the same game.
To be fair, even if there had been rules, Butch wouldn't have cheated in the knife fight. He cheated immediately before the knife fight.
Subverted in Talladega Nights: The Ballad of Ricky Bobby. Not only is there a rule against getting out of the car and running, but they're both disqualified for it. Double subverted in that neither cares, and still count it as a moral victory for Ricky Bobby.
Still, NASCAR rules work much differently in real life. In the 2009 Aaron's 499 at Talladega, Carl Edwards was turned by Brad Keselowski in the tri-oval on the last lap, clipped Ryan Newman, and flew into the catchfence as Keselowski and his Nationwide team owner Dale Earnhardt, Jr. crossed the finish line 1-2. After coming to a rest on the track, Edwards climbed out of his car and sprinted the rest of the way to the finish line before taking a mandatory ride to the infield care center. He finished 23rd, first car not on the lead lap, and was not penalized.
If such an incident happened the way it does in the movie, the race would be over the moment the two cars flipped, and NASCAR would utilize video replays and scoring loops to determine which car was in front at the instant the caution flag waved.
In the 1986 film Lucas, scrawny 14-year old Lucas Bly takes advantage of a school district rule that says that school sports teams must allow any child with an interest to play in order to join the school football team in a misguided effort to impress the girl he has a crush on. The coach is reluctant, as Lucas can best be described as "scrawny", but it forced by the school district to let Lucas onto the team. The first time he actually plays, though, Lucas is injured so badly he requires hospitalization. There might not be a rule against scrawny runts joining a football team, but maybe there should be.
Several times in Fright Night (2011). Vampires can't enter residences without an invitation, but there's nothing against pretending to be delivery boys, attacking victims in abandoned houses or blowing their homes up.
Griphook:I said I'd get you in. I never said anything about letting you out!
In Lord of War, the Interpol Agent pursuing Yuri accuses him of exploiting a loophole in international arms trading laws by shipping military vehicles and their armament seperately so they don't count as prohibited/embargoed heavy weapons.
In the Name of the King: A Dungeon Siege Tale has, apparently, a requirement for the magi that they must serve a king for them to be able to use magic. Gallian reveals that the beastly Krug have no king, so he simply crowned himself as their king. Thus, he serves the best master he can think of - himself. The rules never specified it must be a king of humans or that the magus himself couldn't be king. Of course, it's also implied that only a madman like Gallian could have accepted such twisted logic enough to allow his powers to work. And Gallian doesn't deny that he has gone mad but actually uses his madness to boost his power.
In Jack the Giant Killer whoever wears the crown of King Erik controls the giants. However, this does not make them entirely obedient, and they could find ways of killing the wearer of the crown indirectly, or simply standing by and allowing the wearer to be killed.
Alvin and the Chipmunks: The Squeakuel. Apparently there Ain't No Rule against a football quarterback throwing the ball with a teammate also holding onto it, which is the only way Alvin's game-winning touchdown is allowed. Granted, such a rule is likely not needed given one would have to have the strength of Hercules to throw the ball and another player together unless said other player was, well, as small as a chipmunk.
Actually, there is a rule against assisting the ballcarrier's forward progress, you can't push him from behind, or throw him (e.g. Over the pile at the goal line.)
In Down Periscope, Lieutenant Commander Dodge fired off two torpedoes at the conclusion of a war game right before a targeting solution from the opposing ship destroyed his submarine. The win condition was to destroy the target in the harbor those torpedoes hit.
Note that the loophole abuse was not winning posthumously; Dodge was intended to play the role of a renegade who might very well be making a suicide run. The loophole was winning by destroying the target. The normal wargame rules of engagement specified to compute a standard firing solution for a torpedo and radio it over, on recipient of which everybody would agree the targeted vessel is "dead". Dodge realized his submarine couldn't survive long enough to go through that process. He also knew his target was an unmanned mockup and that he had two live torpedos which could be fired without proper programming and which had some chance of hitting the intended target and a good chance of missing everything else in the harbor. He got lucky.
In Thor, Heimdall is ordered by Loki to not activate the Bifrost for anyone. When Sif and the Warriors Three need to help Thor out on Earth, he sticks his sword in the controls and leaves, essentially leaving the keys in the ignition for them. Later, he takes advantage of having taken an oath to obey the king. When Loki, the acting king, fires him, Heimdall attacks, no longer being bound to obey him.
Heimdall is good at this, doing it again in Thor: The Dark World. It's his sworn duty to notify Odin of crimes against the throne. So he calls Odin to the Bifrost to report Heimdall's OWN crime, i.e. luring Odin away from the palace.
In Bad Words - a former loser of a spelling bee finds and sets out to exact revenge after learning that a certain age isn't listed for an upcoming spelling bee.