My interpretation was a little different than yours. When other characters try to move Mjolnir, it doesn't move at all. When Captain America tries to move it, it moves.

I think he probably doesn't pick it up, because he knows this is supposed to be a light-hearted moment, and he doesn't want to cause Thor any embarrassment, or cause conflict. Now he knows he's worthy, Thor knows, and he's made his point.

I guess we'll see when the movie comes out...

Captain America COULD be worthy, but in that moment, NOT worthy enough to wield the hammer. When Mjolnir has been wielded by others, it is usually a moment of extreme peril and then the "almost worthy" can level up, temporarily to become "worthy-for-the-moment."

• Several times in the canon Marvel Universe, Mjolnir has been lifted by Captain America and others but this is usually "in extremis." These would be situations where the Hammer is what is needed to solve the problem and the enchantment is temporarily lifted so that a "nearly worthy individual" can make the grade.




• Captain America and Superman have both "made the cut at least once."

• But as Thor points out a few seconds after the action has ended: "There is an enchantment 'pon my hammer laid by my father Odin. It is not... easily lifted by others. My father is stern, Superman. But not stupid. A very few worthies have been allowed to over come the spell, in desperate hours. But know this. Perhaps it was but briefly... but it was in good hands."

See also: What will happen to “the enchantment of worthiness” on Mjolnir after the death of Odin?

Because Steve Rogers isn't worthy, yet...

Being "worthy" is pretty sketchy and is discussed to death, but the scene that actually explains this best is from the very end of Age of Ultron.

Steve Rogers: But if you put the hammer in an elevator?

Tony Stark: It'll still go up.

Steve Rogers: Elevator's not worthy.

Steve is jealous of The Vision and wants a reason why he couldn't, we expect as much from Tony, but Steve feels cheated that he "wasn't worthy". During the party he wanted to wield the hammer to show off, little more. Now Mjolnir wiggles, because we know Steve is a good person, but right then and there, his intentions were less than worthy.

Steve wanted to wield the hammer for the very same reason that Thor did when he landed on Earth:

And Thor failed here too, so why could the Vision wield it? Because he wanted to hand it to Thor to get the Avengers moving against Ultron and immediately handed it off. The Vision didn't necessarily want Mjolnir, he wanted the Avengers to work together - thats what made him worthy.

So, after watching Avengers: Age of Ultron we now know that in MCU

Vision is consistently worthy of wielding Mjolnir, even if there is no special need or peril

and thus we can disregard any notions that it requires a moment of peril. Outside of MCU Captain America was worthy of wielding Mjolnir twice in moments of great peril, so that is where the theory came from, but for the above reason that same logic would not apply to MCU.

Now, regarding the most upvoted theory that Captain America didn't lift Mjolnir to prevent putting Thor in a hard position:

I didn't see any indication of that in the rest of the movie and I think that if that was the intended idea it would have been made abundantly clear. Do please correct me however if I am wrong, because I did not pay special attention to this.

So what does that leave us with? Honestly, I think the fairest assessment is that within the boundaries of MCU it has not been made clear why he was only able to partially move Mjolnir. One would expect it to be a binary thing: Either one is or one is not worthy to wield Mjolnir. I believe that is why Mark Bessey's theory has a lot of merit, however at best that is for now just a fan made idea.

brave, not selfish, legitimate leader, prompt to sacrifice

The same can be said about Tony Stark aside from the not selfish part. He's brave, Tony's usually the first to face off against an enemy. He's a legitimate leader, he's actually the one who rallied the avengers to Cap's side in the first movie. He's also prompt to sacrifice. Remember who saved all of New York and all of the Avengers from a nuclear blast?

But more to your question. This version of Captain America isn't the same as his comic book counter-part. In the comics, Cap is perfect, or as close to perfect as he can be. In the MCU, this isn't the case. Sure, Steve is a very good human being, but he suffers from major flaws. He's extremely arrogant, almost on Thor's level from the movie Thor.

In the MCU, it's clear that Steve considers himself better than every other human on the planet. Some of his lines from the Avengers shows that. "Big man in a suit of armor, take that off and what are you?" This line alone is incredibly insulting. He's not only telling Tony that he's nothing without that suit of armor, but basically that anyone Steve feels is beneath himself is nothing. It's the equivalent of saying something along the lines of "Oh, you never served your country or gave back to your community? You're beneath me."

Again, yes, Steve is brave, heroic, and selfless, but these qualities aren't what make someone worthy. Remember, Thor had those same qualities, as does Tony(aside from the selfless part). What made Thor unworthy in the first Thor movie was a combination a a few things. His arrogance, dude thought he was untouchable, better than everyone else on Asgard, and above the law due to his heritage. Cap is almost just as arrogant. Thor also wasn't humble in the beginning. He never recognized others for assisting him, it was always his achievements, no one else's.

Cap is also extremely self righteous. Watch most of his arguments or confrontations with anyone in the movies. In his head, he's always right, it's his way or the high way and if you don't agree with him, you're wrong, end of story. This is evident by his guilt tripping of Bucky in CA:TFA. Yes, Steve was trying to do his part to help the country, but he flat out made Bucky feel like shit for trying to dissuade him from enlisting.

Bucky was trying desperately to save Steve from embarrassment, prison, and probable death. Bucky was being a good friend and even suggested other ways Steve could help the war effort, something Steve actually scoffed at(again, even before he went through the Super Soldier program, he thought he was above certain people and certain things). Like I said, he made Bucky feel horrible for trying to protect him, all because Steve felt he was right and above working in a factory to produce supplies for the troops.

Steve: "What do you want me to do, collect scrap metal in my little red wagon?"

Bucky: "Yes!"

Steve: "I'm not going to go sit in a factory. Bucky, Bucky, come on, there are men laying down their lives. I got no right to do any less than them. That's what you don't understand, this isn't about me."

Bucky: "Right. Because you got nothin to prove."

This dialogue clearly shows that Steve doesn't believe that doing something like this is worth while. Sure, his words can be considered patriotic, but Bucky sees right through him. Steve's motivations to join the military are entirely self-centered. He feels he has to prove something to the whole world. He's basically saying, "You want me to join the women folk making weapons and shoes while all the men go out and fight? Phhp. please, I can fight just as well anyone else, just watch." In face, we can add a few more unworthy qualities based on this alone. Narcissistic, self-centered, sexist....I'm sure there are many more that can be added, but I think we're around a half dozen traits that would make MCU Steve unworthy.

Now that I think about it, MCU Captain America is actually a douchebag, even more so than Tony Stark or Thor.

Steve's arrogance shows multiple more times in the movie. Ordering Col. Phillips to give him names and information, you're a Captain dude, not God. Again, The hell I can't, I'm a Captain. Pretty sure Peggy Carter's position was much higher than a newly promoted Captain.

His self righteousness is on full display in the Avengers as well. In the scene where he discovers that SHIELD is using the Tesseract to make weapons. He blatantly doesn't care that Earth's weapons are nothing compared to people like the Hulk or Thor. He doesn't care about the fact that if the Hulk were to go on a world wide rampage, that no one could stop him with their current weapons. Or if Asgard or another civilization were to attack Earth, humanity would be utterly defenseless. None of that matters, all that matters is that SHIELD is using an energy source to make these weapons. Nevermind the fact that it can advance humanity. All Steve saw was HYDRA weapons and designs and remembered what they could do. Even Fury's explanation as to why they were using the Tesseract went through one ear and out the other. To Steve, he was right, period, end of story, humanity's defense be damned.

These are the glaring reasons why Captain America is not worthy to wield Mjolnir in the MCU. He's extremely arrogant, self righteous, narcissistic, self-centered, sexist, prideful, and thinks of himself as above everyone else. These are the exact aspects that made Thor unworthy to wield the hammer in the first Thor movie. It wasn't until Thor dropped his pride, arrogance, self righteousness, and accepted his own humanity that he was able to re-wield Mjolnir. I imagine by the beginning of Age of Ultron, Cap will have started to lose his arrogance, pride, and self righteousness, which is why he's able to move the hammer, but not yet pick it up.

My personal theory is that Mjolnir is more than just a hammer, it's a very advanced piece of ancient celestial technology, and contains something at least equivalent to a weak AI.

We see in Thor that the hammer is able to respond to voice commands from Odin when it is given instructions, and it is intelligent enough that it is able to determine when Thor has become worthy to wield it again and is able to propel itself to him.

It is safe to say that there is no actual "magic" in the MCU*, just technology and knowledge that is indistinguishable from magic, and so an intelligent hammer is believable.

This means it decides who it will allow to lift it, and who can't. It's not just inanimate objects, otherwise the truck with the tow rope in THOR would have been able to move it from the impact site. It can move and direct itself, and so if it wants to stay in one place it does. If it wants to move it does. If it wants to be picked up by someone then it allows it.

The hammer itself wanted to show the Avengers that Vision had it's blessing, so it allowed Vision to pick it up to get the point across. That doesn't mean Vision would always be able to lift it.

This actually makes the scene with Cap trying to lift the hammer a little more amusing; If the hammer is intelligent, could it have wobbled a little just to mess with Thor?

* Even in Dr. Strange when the Ancient One is describing how they do their "magic", she says something like "What you call spells is the programming language of the universe, powered by energy channeled from other dimensions..."

My interpretation is that although cap is worthy it is still Thors hammer and he is alive and well. Cap can not fully lift the hammer then because he would simply be showing off, if he were to lift it to be able to protect someone he would be able to.

Captain America is mortal, so is Thor but in a different way. There seems to be a form of energy exchanged between Thor and Mjolnir that is not there all the time between anyone else and Mjolnir. It could very well be what makes Thor worthy and no one else until Thor is to far out of the fight.

In the movie, Captain America tells Tony Stark that he has a dark side, just nobody's seen it yet. Captain America's yet unseen dark side could possibly be why he isn't worthy.

I think Steve is very much worthy of Mjolnir, but at that particular moment had too much self-doubt about himself and his ability to lead the team. He doesn't believe he is better than everyone else, he actually has self-esteem problems that always thinking he is not doing enough. Thor was deemed unworthy because of his self-centeredness in his first movie. Once he was going to give his life selflessly for others, the Hammer responded once again. Cap is sometimes haunted by the fact that he can't save everyone and that he may not be doing enough to help people. These doubts are probably effecting his "worthiness" as decided by Mjolnir. Other than that, he would be worthy.

I realized I'm a bit late to party here, but I stumbled in because the same question was bothering me. But the theory that I've come up with now is that it was circumstantial. Cap could lift the hammer in a different context, when he truly needed to, the same way Vision is able to lift the hammer in the movie because he needed to. The team wasn't sure if he could be trusted, they weren't all sure if he was truly on their side. The hammer allowed itself to be lifted to prove that Vision was worthy.

I like to view this in a bit of a different way than most. In my little world, Thor was grinning as each Avenger made an attempt, but was actually expecting Steve to lift it. When he failed to do so, the grin disappeared...

To update as of Avengers: Endgame

Captain America is indeed worthy and uses Mjolnmir in the battle against Thanos.