In The Empire Strikes Back, when Han is about to get frozen in carbonite, Chewie starts to freak out and throws some Stormtroopers off of the platform.
The camera cuts to a shot of Boba Fett lifting his gun to shoot Chewie and then Darth Vader grabbing the gun and pushing it down.
Why would Vader do that?
Here's a a GIF of the moment this happens:
Vader did that to protect the carbon freezer, which he needed for Luke, and to protect his hostages whom he might have wanted to put to... other uses. Vader could have lured Luke into a trap using the hostages. He could also have extracted information from them. They could have been used as additional test subjects as well, should Han's carbon freezing have failed.
My theory is that Vader can hear C-3P0 and re-awakened a bit of Anakin. 3P0 is in pieces on Chewbacca's back and will be destroyed if Chewie falls to his death.
Boba Fett raised his gun in reaction to Chewie's loss of composure when it became clear what was going to happen to Han. Han, Leia, and Chewie were each in restraints, fully surrounded and outnumbered by Vader and Lando's men, and Chewie was quickly subdued by the stormtroopers and Han's words. There was no risk of escape, and even the armed stormtroopers didn't raise their guns. Vader was simply preventing Boba Fett from overreacting and making the situation worse.
If Boba Fett had fired, it would have created an even greater commotion and cause Leia and Han to fight back. If Boba had missed and instead hit the stormtroopers trying to restrain Chewie, then that would have potentially given the rebels an actual chance to escape or at least created a greater hassle for Vader.
So Vader acted rightly when he stopped Boba Fett and let Han calm Chewie down, retaining the cooperation of his prisoners.
After much research, I've finally found an answer to this one in the "Once Upon a Galaxy - A Journal of the the Making of Star Wars : Empire Strikes back".
As recounted by Alan Arnold, the original reason that Chewie and Leia were in the chamber was to act as leverage on Han Solo to remain compliant when testing out the Carbon freezer.
Had Fett killed Chewie, Han would likely have either tried to escape or at the very least injured himself trying to kill Fett, rendering him useless for the test. Vader prevented this, sensing that the situation could be brought under control.
(Now the scene is Kerch's [Irvin Kershner] trailer. Harrison has arrived to talk further about the scene to be filmed this morning. It is 11 A.M.)
IK: You see, Harrison, one thing I discovered that is going to affect us crucially is the fact that you have no way of knowing that you are the one they are going to put in the carbon freeze. They bring all three of you in, but you don't know anything. The princess doesn't know anything. She just senses danger. None of you has ever been in this place. You don't know what this place is. That's the reality of the situation. So we have to add some lines.
HF: Yeah, there's something missing.
IK: Right
HF: I don't have any lines. I'm on my way to an appalling fate and, well, it's no time for a speech, but surely I should say something, try to talk my way out.
IK: You've got heavily armed people all around you. Why do you think that Chewie and Leia have been brought in, too? I know why they are brought in. It came to me last night. They are brought in so you will not make problems. If you try to make a break, if you try to jump them, try to do anything so as not to go into that pit, they'll kill Chewie and Leia, too. They use them to subdue you.
HF: But they don't use them well enough, do they? Chewie tries to fight them off, but I don't raise a hand to help him.
IK: No, actually you stop him so he won't get himself killed.
HF: But I stop him before I know that if he fights he'll get himself killed. It's in Han's character to join Chewie in the fight. The bargain I'm likely to keep quiet for is if I'm convinced that Leia is safe because Lando has taken a shine to her.
IK : So we need another scene
If you notice, Leia makes eye contact with Vader and wonders why. I think Vader senses something about Leia. That maybe she's his daughter and if he kills Chewie then she wouldn't have protection.
I agree, I have always wondering why he would save Chewbacca and I came to the conclusion that he didn't. Leia is hugging Chewie and Fett could have shot her. Vader probably had an uneasy feeling while on Bespin in close contact with Leia. Fett's raising his gun probably triggered an instinctive reaction to protect his daughter. He probably didn't even realize she was his daughter until the reaction was triggered.
In support of my theory - he immediately changes his mind about leaving her on Bespin and orders her to be taken to his ship. Also, it is after this that he tells Luke that he is his father... Maybe it all came together for him at once. How else would he know?
No No No, Darth Vader stopped Boba Fett because part of the deal he made with Lando was to protect the others... And don't you remember when Leia told Lando that Vader wanted them all dead, and the Lando said he didn't want them at all and Vader was only after someone named Skywalker...
According to the film's official junior novelisation, Vader's concern was that in his eagerness to shoot Chewbacca, Fett could hit either Leia or Han, both of whom have intrinsic value.
Realizing what was about to happen, Chewbacca let out a wild howl. He threw his right arm out to his side, striking a stormtrooper with enough force to launch the figure from the elevated platform. Before anyone thought to react, Chewbacca lashed out with his left arm and disposed of a second stormtrooper in the same fashion.
Across the platform, Boba Fett brought up his blaster rifle, but Vader — hoping to preserve his other captives — lashed out and grabbed the rifle’s barrel, forcing the bounty hunter to aim away from the melee.
Interestingly, this is (somewhat) contradicted in an earlier Q&A with Pablo Hidalgo in Star Wars Insider #75, where he says that Vader's main motivation was simply to remind Fett that he'd already told him not to shoot without orders.
Q. In The Empire Strikes Back, why does Vader stop Boba Fett from shooting Chewbacca in the carbon-freezing chamber? Was it the fact that C-3P0, Vader's droid, was attached to Chewie’s back?
Although a stirring short story that appeared in Star Wars Tales #6 suggests that Vader did indeed recognise C-3PO on Cloud City, there really was no connection between the Dark Lord and the golden droid back when Empire was made. Vader's restriction of Fett was primarily meant to show just who was in charge and that no-one fires a shot without Vader's say-so. Granted, it's hard to read expressions through immovable plasteel armor, but it looks more as if Vader is reminding Fett about his “no disintegrations” order than as if he’s having gooey memories about a protocol droid he once built.
Vader stopped Fett from firing because Vader was still in control of the situation, and he didn't need Fett to shoot Chewbacca. He was continuing to dominate the situation and get what he wanted, the way he always did. Vader's intention was to get Luke to join him, and part of his plan was to lure Luke using his friends and making them suffer, and not to kill off Luke's friends. Chewbacca wasn't going to get away, or overpower Vader, and the armored stormtroopers he tossed were probably just bruised and aren't important - he had plenty of them around.
Yes, Luke was already on the way, but that didn't mean their suffering wasn't still useful as bait.
And, since Vader wanted to convince Luke to join him, not killing his friends might be helpful.
The reason is clear, Vader senses the importance of the moment: Leia and Luke together with their father. This is an act of mercy, though he is not aware of the full significance (he doesn't realize Leia is his daughter till act 6) he senses the familial relationship and acts quickly to ensure everyone's survival. This is Vader's first act of humanity since turning, propelling him toward the climax of act 5 ("Luke I am your father") and the ultimate redemption of his spirit.
I think Vader stops him because of a combination of the two reasons given above. Firstly although Vader clearly respects Fett, it's made clear that he also distrusts him somewhat. Vader is a dark lord of an empire Boba Fett is a member of a sleazy criminal underworld who's happy to spend his retirement living in the debauched palace of Jabba the Hutt, he's obviously ruthless and violent and doesn't live by any sort of code that Vader does. So Vader stops him from an impulsive potentially reckless violent act and also shows who's in charge between them. However the waythey cut the scene to show Leiah making eye contact with Vader as if to ask him why he saved them, and Fett giving Vader a strange confused look afterwards clearly shows one of the saga's first signs of his good side. I don't think George Lucas had any idea about the backstory between Vader and C-3P0 at the time of making EWmpire Strikes Back, but the backstory with Leiah and Luke was clear. He felt the impulse to protect Leiah.
It has nothing to do with the Force, anger, or Leia being his daughter. After escaping from Hoth and being pursued by Vader and the Imperial Fleet, Vader contracts several bounty hunters to aid in finding the Millennium Falcon. He tells them all that:
You are free to use any methods nessesary, but I want them alive! No disintegrations!
He says this directly to Boba Fett who in turn tells Vader:
As you wish.
Basically as stated above, it is Vader's law. Once he saw Boba Fett breaking his order he physically stopped him.
It's hard to say. I do believe vader has a mistrust to boba fett. Think about it. Boba is the clone son of jango. Jango had a hit on padme which is annakins wife. Seeing boba raise a weapon reminding him of padme and luke and leia being together in his presence had to show him something familiar about them to him. Vader had everything from episodes 1 2 and 3 in front of him at the same time. Including 3po the memory of his wife and the feeling of needing to protect these two unfamiliar but yet comforting people of which he felt the force in both. And boba fett the son of the bounty hunter who tried to kill his wife. Whom of which he never got to confront
I've thought long and hard about this. I think all of the responses here are great by the way, and have good insight. I've come to the conclusion that really this is shown as a kind of display of character between Vader and Fett. Really, its just as much about showing how off the hip Boba Fett really is. We get to see him without hesitation, ready to kill, to the point where even Darth Vader is uncomfortable. So in a sense, Lucas is showing just how brutal Boba's character truly is. Because if you have Vader holding you back from making a move; you're pretty much a hard ass gangster.
Beyond that, we see how Fett's violent behavior is juxtaposed against Vader's highly controlling and calculated personality. He shuts Fett down with a firm strong arm and puts him right back where he wants him, almost as if to say "I didn't give you permission for that. This is my plan." Vader is fully in charge and doesn't want things to go anyway other that what he expects. He's decided he wants Chewy and Leah alive, until HE decides that they die. Until then no one will step over him, and he will use their lives as leverage.
I think it's important to note, that Vader is instinctively realizing that he has a connection to Leah as well, and he's dealing with that only semi-consciously. She looks directly at Vader right after that moment and slowly walks over to Chewy to calm him. It's as if she and Vader have some understanding about that moment, and she knows she must assist Vader in making things calm again.
I believe he stops Fett because he needs Leia and Chewie alive to lure Luke to the carbon freezing chamber. So he protects them. Knowing Luke was comming. His best friends were the only bait. When Leia looked at Vader I think she sensed somthing in him through the force. So if she did he must have felt somthing as well. So those reasons are why he protected her and Chewie.
Vader stops Fett because he wants Leia and Chewie, two prominent members of the Rebel Alliance, as his prisoners. He later, despite Lando's protests, orders for them to be brought onboard his ship, later still, when he expects the MF is going to be tractored and boarded he gives orders to set weapons to stun - he clearly wants all of the rebels alive.
So here's why, it's because in the Clone Wars animated series Chewy and his people save Anakin's Padawan, Ahsoka Tano. There you have it. Season 3 Episode 22.
I'm pretty sure Vader stopped Boba Fett because he 'felt' Chewbacca's anger through the force, and it felt pretty good to him. Please remember, Darth Vader was a Sith Lord and as such was always (at least since his turn to the dark side) a master of evil. ;)
