If you are evil enough, one way to turn someone to your side or motivate him to stay there is to threaten to hurt someone he cares about. This "friend" might indeed be the target's best friend or a love interest; however, if the target is the kind who tries to protect everyone, almost anyone may serve as a hostage.
This trope is a signature tactic of a Bad Boss. It is also a form of Villainous Demotivator. Those who have their friends and loved ones under constant threat should they fail might be driven to greater efforts. In some cases, it may not be possible or feasible for the villains to harm the ones they are trying to "motivate." However, in the long run this situation can hardly be good for morale or loyalty to the Big Bad. The target may, and likely will, perform a Heel-Face Turn should the opportunity present itself (and it will) in a desperate bid to save their family and themselves from their circumstances. This can be a factor in convincing people that The Mob Boss Is Scarier than the police.
Can be Played for Laughs if the "friend" is someone the hero doesn't like.
Compare Even Mooks Have Loved Ones, where the Big Bad doesn't directly target his underlings' loved ones but merely shows callous disregard for them. If you actually punish his friend for his failure, that's a form of Revenge by Proxy. See also Blofeld Ploy.
In the Water 7 arc, the CP9 make Robin help them in obtaining the blueprints of Pluto in order to spare the lives of the rest of the Straw Hat Pirates.
In Luffy's flashback arc, Sabo's father forces him to come home by threatening Ace and Luffy's lives, and tries to get him to deny his involvement with them in that same way, but ends up having to bribe the official.
In the Fishman Island arc, Hody Jones claims that he has a kraken's brother hostage and will kill him if he refuses to fight against Luffy.
In a flashback in the Arlong arc, Nami is told at one point that if she doesn't do her work properly, Arlong will bring in and kill a villager in front of her like she did with Bellemere. He also gives her an ultimatum midway through the battle for Arlong Park; come back to him and he will spare everyone except Zoro and Sanji, or refuse and watch her entire village die.
FUG from Tower of God coerces Viole to work for them this way.
A particularly brutal version happens to Yuri in Angel Beats!. When she was younger, some crooks broke into her house while her parents were away. They then took her 3 younger siblings, and told her that they would kill one of her siblings every 10 minutes if she didn't give them something valuable. She tries but fails, and the cops arrive 30 minutes later...
In the introductory arc of YuYu Hakusho, one of the teachers tells Kuwabara that if he and his friends don't stop fighting and get their grades up, one of his friends will have his work permit revoked. Then, after Kuwabara keeps his end of the deal, the teacher tries to deliberately misgrade his tests so that he won't have to honor his end, and possibly to force Kuwabara into hitting him and actually violating his end of the deal. He ultimately gets found out.
In Yu-Gi-Oh!, for the climactic battle of the Marik arc, Evil!Marik makes the board a setup which is basically this plus a Sadistic Choice. He pulls Yugi's soul and Normal!Marik's soul out of their respective bodies and hangs them up in the air. When the dueler loses life points, bits of the other's body are removed, and the loser's normal side goes to the Shadow Realm.
In Yugioh Zexal, No.96 sets up a duel with Astral that if No.96 loses life points, Vector will set up another dangerous trap for Yuma to die from.
Smythe in the Secret Six likes to keep his slaves in line by slaughtering everyone around them to teach them a lesson. Do as he says or people totally unrelated to your failure will get horribly killed.
A variation is inflicted on Laura Kinney AKA X-23, after her mother/creator helps her escape from the Facility. Laura is hiding out with her aunt Debbie and cousin Megan, when Kimura tracks her down and recaptures her. Kimura then intends to punish Laura for escaping by torturing her cousin and aunt to death and making Laura watch. She even gives Laura a Sadistic Choice as to whether Megan dies quickly or slowly, before summarily deciding to slowly push her finger into Megan's chest intending to tear out her heart. Fortunately, Laura manages to escape and rescue them but there's no question Kimura would have gone through with her threat.
In the Portal 2 fanfic Blue Sky, GLaDOS uses Atlas and P-Body to capture the entire population of the town Chell has settled in, threatening to kill them if Chell does not cooperate and do the testing.
It's implied that Professor Moriarty threatened to kill Holmes in order to coerce Irene Adler into cooperating.
In the sequel, he kills Irene Adler and sends men to kill Watson and Mary, even after Holmes personally tells him that Watson will no longer be a part of his investigation. Of course, this ends up biting the bad guy in the end, as Watson ends up stopping his assassin, which he wouldn't be doing if he was still on his honeymoon. It's also the same threat that ends up forcing Holmes to grab Moriarty and jump into Reichenbach Falls.
In X-Men Origins: Wolverine Stryker forces Kayla Silverfox to conspire with him this way by threatening to kill her sister, Emma Frost.
In the film Full Metal Jacket, the first part of the film is about the training of the new recruits in the US Marine Corps. One of them, nicknamed "Gomer Pyle," can't seem to improve in his training, so Gunnery Sergeant Hartmann stops punishing him and starts punishing everyone else. The other recruits take it out on him in the infamous "blanket party" scene, where they pin him to his bunk with a blanket and beat the crap out of him with bars of soap wrapped in towels. After this, Pyle starts to show improvement in his training, but also starts to develop a psychotic breakdown, ultimately culminating in the murder of Hartmann and his own suicide.
In Under Siege, the Big Bad is having his Mooks lead the crew of the captured battleship into the hold. On the way, one crewmember assaults one of the criminals. Not only is he shot for his trouble, the Big Bad immediately shoots the guy next to him, claiming this is the price to pay for disobedience.
In Die Hard, John McClane is messing up Hans Gruber's plans. John's wife's coworker (whom he met once) tries to get in Gruber's good graces by attempting to talk his "friend" McClane into giving himself up. McClane, fully aware of what kind of a person Hans Gruber is, tries to get the guy to admit he's lying but to no avail. Gruber smiles, and shoots the guy for his trouble.
In Time Limit an officer has made propaganda for the North Koreans while a POW and is going to be court martialed. One officer wants to know why and finds that after the one POW who betrayed the other men was strangled by the man who drew the short straw, the Korean commander called in the ranking POW and told him that he was going to do everything he was told or the other sixteen men would be taken out and shot right in front of him. He gave in.
In the second Rambo movie, Rambo is captured by the Soviet "advisors" to the Communist Vietnam commanding officer. The advisor takes Rambo's knife and puts it into the charcoal fire heating his tea. When Rambo won't divulge the information requested, the advisor threatens to stick the now-glowing tip into the eye of the American POW with whom Rambo was captured.
In Biloxi Blues, Sgt. Toomey routinely punishes Wykowski whenever Eugene fucks up. Subverted in that Wykowski is not Eugene's friend, but the biggest, most ill-tempered soldier in the platoon.
In Crimson Tide, the USS Alabama's Captain, played by Gene Hackman, needs the Weapons officer, played by Viggo Mortensen, to open the safe where the missile firing trigger is kept. When Weps refuses, the Capt gives him 5 seconds to comply, threatening to shoot him. Then he realizes that if he does, he still won't have the combination. So, he threatens one of Weps men, who doesn't know the combo. Weps complies but it gave the XO time to remove the firing key on the bridge.
In The Grey Zone, the Nazis resort to interrogating a female prisoner in the death camps who smuggled in powder for the upcoming uprising of the Sonderkommandos by lining up all the other prisoners and shooting the women one by one unless she talks. The officer threatens to clean the entire block out and move on to the next one until she cooperates, but she kills herself by running into the electrified fence when they prepare to shoot a teenage girl.
In The Shamer's Signet, Dina is forced to use her Shamer powers on anyone her captor sees fit, for trivial things. If she refuses, he'll kill Tavis, the random kid who was with her when she was kidnapped.
This is a popular tactic of Lord Voldemort in the Harry Potter series.
In The Neanderthal Parallax series, serious crimes in the Neanderthal world are punished by castration of the offender and all others who share at least half his genes (parents, siblings and children).
The children's book The Whipping Boy is based on the 15th century real-life practice of punishing a companion to a prince as the royal line was considered divine and only another from the royal line could do the punishing on pain of death. In real life, a whipping boy would be a lifelong companion to the prince so that their emotional bond would make the whipping a real punishment for the prince. In the book, the whipping boy was chosen to start a new life in the castle with the young prince, who was a Royal Brat. This trope is played with, however as when the two are kidnapped, the whipping boy is more educated than the prince, so believing the prince to be the whipping boy, he is the one punished.
Sergeant Grimshawe in Kim Newman's Alternate History novella "Teddy Bear's Picnic", being the setting's version of Gunnery Sergeant Hartmann, does this.
Routinely used by President Snow to intimidate the tributes in The Hunger Games. Katniss figures out that safeguarding her family and friends is important in order to be able to stand up to Snow. However her entire district is then razed in retribution for her and Peeta's stand against the Capitol.
In The Dragon Revenant by Katharine Kerr, the head of slaves tells a tale of how when he was a boy, a slave in the house opposite killed his master. Every slave in the house was put to death, including mothers with babies-in-arms. That was one of the ways Bardekians controlled their large slave population.
A common tactic of the People's Republic of Haven in the Honor Harrington books: commanders who lost battles could expect to be executed along with their families.
Southland: This happens in the episode "Derailed". Marta Ruiz, the matriarch of the Avenue drug gang, wants Janilla dead for agreeing to testify against her sons for a drive-by shooting. Marquece, Janilla's ex-boyfriend and a member of the Grape Street gang, after being taken into custody, reports to Marta that the police have her and that he doesn't know where she is. Marta reminds Marquece that the Grape Street gang owes Avenue money, and after Marquece promises to fill her in on Janilla's new location as soon as he finds out, Marta threatens to have Marquece's entire family killed if he screws up again.
Anya wants to undo a wish she granted as a vengeance demon that killed an entire fraternity. D'Hoffryn, her boss, says it will require the death of a vengeance demon and Anya offers herself, as a way to repent for her sins. Then D'Hoffryn summons up Anya's friend Halfrek and casually kills her.
D'Hoffryn: Never go for the kill when you can go for the pain.
Invoked as a threat in 'Lover's Walk'. Spike, distraught over his failed Unholy Matrimony, kidnaps Willow and Xander and forces Willow to make him a love spell. Made oddly terrifying by how heart-broken and depressed Spike is.
Spike: And if at first you don't succeed ... I'll kill him, and you can try again.
On Law & Order: SVU to keep child slaves in line the mistakes of one would be punished on all of the others. This ensured the kids wouldn't run away when sent out to work or prostitute, because they were certain the others would be beaten or even killed if they ran.
In a double example, the White Collar episode "Front Man" has Neal being coerced to perform a series of tasks for a gangster, who threatens to kill his hostage (a young girl) if he refuses. While doing the first task, he is told that if he doesn't get the required information from a female travel agent in a certain amount of time, a sniper will kill her (the travel agent). You can even see a red dot appear on her head and clothing occasionally, reminding Neal of his deadline.
Toward the end of Season 7 of 24, Tony Almeida and his men break into a Muslim illegal immigrant's apartment, take his brother hostage, and tell him to do as he says if he wants his brother to live.
Minnie in Lark Rise To Candleford has a stepfather who uses this tactic to brutalise and subjugate his wife and her daughters.
A non-villainous example occurred on The Mentalist: the new boss, in an attempt to get Jane to at least think a bit more before he acted like a complete jerkass, informed him that if he screwed up, nothing would be done to him; Lisbon would be canned instead. For once Jane is rendered completely speechless.
After Teal'c betrays his god Apophis in the pilot episode of Stargate SG-1 to help humans, he finds out that his wife and son were exiled from their home (which was burned and branded with the symbol for "shol'va" - traitor). They are forced to live on the outskirts of the village as untouchables. When his son reaches the age of joining, Teal'c wife has to beg the priests to allow Rya'c to undergo the ritual. It took her to finally divorce Teal'c and marry a friend of his in order to wash away his "shame".
Dexter: In Miami Metro Police Department, Captain Matthews exploits Lieutenant (later Captain) LaGuerta who is the head of Homicide. Her close friend and later lover, husband, and Amicably Divorced ex-husband Sergeant Batista is the one who suffers — or is to suffer — for her screw-ups.
The X-Files: At the end of the episode "Drive", AD Kersh gives Mulder and Scully a scolding for saving lives. They had another assignment, completely pointless as they were Reassigned to Antarctica. He threatens Mulder that he will bill Scully for the unauthorised expense, which was mostly Mulder's fault.
Mulder: Why don't you bill me?
AD Kersh: I'll bill your partner instead. You two obviously relish the role of martyr.
Horatio Hornblower: Captain Sawyer gets angry at Horatio for no better reason that his informing him that he's shortening sails (perfectly according to the orders), and not asking him beforehand whether the captain permits that. He decides that he will teach Horatio a lesson by getting men from his division punished. The last man to get down from the mast is to get flogged, which causes panic and a lethal accident, as one poor sailor falls down. Horatio, Archie, Styles and Matthews must scrub him off the deck, and Sawyer even orders them to toss him overboard immediately without a funeral. It is the beginning of Captain Sawyer's Sanity Slippage. He ends up a prime example of Insane Admiral.
In Metal Wolf Chaos, people Richard find to be Metal Wolf sympathizers are killed along with their family members within four separations, their old classmates AND their friends and coworkers. Kevin Bacon is understandably concerned.
In Red Dead Redemption this becomes John Marston's primary motivator after his wife and son are kidnapped.
In Ocarina of Time, after exiling Talon of Lon Lon Ranch and taking the place over, Ingo the Stablehand threatens to treat badly the horses that Malon loves if she goes against him, which sets the stage for Link kicking his ass in a horse race on Epona, who he befriended as a kid earlier in the game.
Officers Tenpenny and Pulaski pull this in Grand Theft Auto: San Andreas, threatening to make sure Sweet dies if CJ doesn't do what they want him to do. Later Toreno pulls this as well but is less malicious about it, and ultimately frees Sweet once CJ has done enough for him.
In Case 5, the Big Bad Damon Gant forces the accused Lana to work for him under the threat of her little sister Ema getting prosecuted for a crime she thinks she's committed.
In the sequel, Maya gets kidnapped by Shelly de Killer in order to force Phoenix to get Matt Engarde a "Not Guilty" verdict, when Engarde was really guilty. Well, he didn't actually kill Juan Corrida, but he did create the circumstances leading to Corrida's death. The player may either get Engarde acquitted, in which case an innocent woman is found guilty and executed, or get Engarde declared guilty, in which case Maya is killed. The only way out is to Take a Third Option and Get de Killer to betray Engarde.
In World of Warcraft: Wrath of the Lich King, you find letters after killing mage-hunter captains of races on your faction (a human and a troll, respectively), reading the letters becomes a very poignant Player Punch when it says that they've been forced to work for the blue flight under threat of their family's death. The reason why Vol'jin is hesitant to openly defy Garrosh is because with the Darkspear Trolls so close to Orgrimmar, it would be easy for Garrosh to send in troops to exact retribution on them, and Vol'jin advises Baine, who has similar positions to him and who is similarly close, to also be mindful of what he says. Vol'jin proves to be correct; he nearly gets killed by one of Garrosh's assassins while trying to prevent Garrosh from bringing back information on making sauroks, and Garrosh has the Echo Isles occupied.
In Scribblenauts Unlimited, the game starts with Maxwell giving a man a rotten apple. As revenge, the man curses Maxwell's sister to turn to stone unless Maxwell collects enough Starites.
Grant: Why do I get hit whenever he says something?!
Girem6: Semantics. Hitting the partner of the offender encourages discipline.
Grant: Oh... well in that case, those boots make you look fat.
[Grant gets hit again]
Grant: Why did I get hit that time?!
Girem6: Because I blame your friend for that comment.
In General Protection Fault, after Nick-Prime sees that Nega-Nick is lying to him about many things about the Nega-verse, including the real reason his plan to have Nick-Prime build Project Velociraptor for his MUTex, Nega-Nick shows him Nega-Ki, strapped to a torture device, and tortures her until he decides to cooperate, saying Nick-Prime can't know for certain that it isn't Ki-Prime he's torturing. Nick-Prime gives in, and Nega-Nick then tells Nick-Prime that one prisoner will be tortured to death in front of him for every hour he wastes. To make matters worse, it is impossible for Nick-Prime to succeed at his task due to Pandemonium's interference.
In Recess, TJ is sent to the Dodgeball Wall for extra punishment, when his friends refuse to bow to the bully Randall.
Slade uses this tactic in Teen Titans to (temporarily and forcibly) convert Robin over to his side. He infects the rest of the titans with nano bots and threatens to kill them if Robin doesn't become his apprentice and follow his every order. Robin manages to Take a Third Option via injecting himself with nanobots, badly harming Slade's pride and forcing him to release everyone.
Though it's never directly stated, it is heavily implied in a few episodes of X-Men: Evolution that the only reason why Colossus is a member of Magneto's Acolytes is because Magneto somehow threatened his family members who are still in Russia.
Tirac from the My Little Pony pilot threatened to kill Spike in order to make Scorpan obey him.
Parodied in The Simpsons. Homer gets tricked into joining the army, and when questioning his sergeant, he forces everyone in his unit to do pushups while he eats donuts, and gets a foot massage from the sergeant.
Homer: I don't get it. How does punishing them teach me a lesson?
This trope is used by most totalitarian regimes:
The Nazis often threatened to kill not only those who tried to resist them, but also their entire families if they tried to defect. This included anyone found harboring Jews in their homes. Erwin Rommel killed himself specifically to avoid this fate after he was found to be complicit in the plot to kill Hitler.
Successful escapes from Nazi death camps were punished by having ten randomly selected remaining prisoners executed, often locked away and starved to death. (i.e., Saint Maximilian Kolbe became a martyr for exchanging places with one of these prisioners.)
It's also the reason that people in show trials confess to imaginary crimes — if they don't, their families will pay the price. The Soviet Union under Joseph Stalin and the "People's Court" of Nazi Germany, among others, were particularly notorious for it.
A story making the rounds in the US intelligence community is about some Chinese exchange students in Soviet Russia, involved in a prank gone wrong. The boys were arrested, and interrogated by the KGB. The interrogation lasted for hours, and the KGB could get nothing. Finally, the Soviets contacted the Chinese Embassy for assistance. A Chinese agent walked into the room, said something to the students, and left. Afterward, the students confessed everything, received whatever punishment was due them, and were sent back to China. Later, the KGB agents wanted to know what the Chinese agent had said to get the students to cooperate. A Chinese translator translated as follows: You will tell the Russians what they want to know. In exchange, you will be killed. If you do not tell the Russians what they want to know, you will still be killed. In addition, your villages will be massacred.
North Korea reportedly has a series of "family camps" where the families of accused political dissidents are imprisoned for being related to the accused.
People in Socialist Czechoslovakia were blackmailed to collaborate with the regime or at least pretend to support the Communist Party through their family, which meant mostly children. Will you not vote? Your child can kiss a good school or a university goodbye. Especially dissidents' children had to forget about studying or getting a decent job. But hey, considering that in the Eighties the intellectual elite was formed by dissidents, they got to hang out with the most intelligent people anyway.
Many of the Latin American drug cartels would do this to those who reported their activities to the police, and even to their own members if they cheated their organization or started informing to the police.
This is often done in military basic training. When one person messes up, the instructors prefer to start with just the offender, but if mistakes continue or they want to make a point, then they get the next guy as well or the whole damn platoon. If the instructors actively dislike you and want you out, then they start punishing the whole platoon except you. When the other recruits are your only support, and the instructors make all of them resent you... either you better be exceptionally mentally tough, or you're quitting (yes, you actually can quit, it's just very hard to unless they really don't want you). The Full Metal Jacket example above is a particularly nasty case of this. Though there is a legitimate reason for it: it's a way to teach the trainees that in a real combat situation, the actions of one affect the entire group. One soldier's incompetence or laziness can get the entire unit killed. It's also used to teach people to look out for one another so they can catch someone else's mistakes: a common tactic in Canadian Military Colleges used to be that if one of the recruit cadets assigned to a room kept having issues during room inspections while the other one or two roommates didn't, eventually the entire room would be trashed to point out to the other cadets that they had a responsibility to look out for more than themselves. Conversely, it is extremely easy to quit the officer accession programs during that period- just say the word and you're out. That's the whole point- only those who can endure it mentally can finish the program and earn the right to lead Marines. Plus they can taunt you with the prospect of quitting. In Boot Camp, the staff is just trying to toughen you up. At the Academy, they really are trying to make you quit.
The original "decimation" — killing one tenth (randomly selected) of a Roman military unit fits this trope well.
In ancient Rome, if a slave killed his or her master, all of that master's slaves would be executed. The idea being that anyone would be willing to risk their own life for freedom, but few would be willing to put the lives of dozens or even hundreds of other slaves at risk.
When Frederick the Great as heir apparent attempted to flee Prussia with a friend, he was made to watch from prison while the friend was beheaded.
In ancient China, a person who committed a capital offense, such as treason, would not only have himself punished, but his family as well. The list of which family members get involved varies from dynasty to dynasty, as does the cutoff age below which children are exempt. The largest list involves the criminal himself, his parents, grandparents, children, grandchildren, siblings, siblings-in-law and uncles and their spouses. The purpose of this long list was to serve as a major deterrent to capital offenses, and encouraged family members to keep tabs on each other and make sure they didn't commit any crimes.
The idea of the whipping boy is that noble children cannot be physically disciplined, so a common-born child would be disciplined in their place, with the hope that this would make the noble child feel guilty. The whipping boy was usually himself a noble. Either from the lower nobility, or a distant cousin, so this method was often an effective tool for teaching noble children that their actions do have consequences and that those consequences will hurt others. The fact that they were forced to watch as someone who had become a close friend get punished for his own actions tended to serve as a deterrent in short order.
A common disciplinary tactic of teachers (sadist or otherwise) in primary/elementary schools is to punish the entire class (denying recess, making everyone stay after class, etc.) for the infractions of one student or a small group. It often backfires, making the innocent students resent the teacher, and doing little to correct the behavior of the actual troublemakers.