The Marvel Cinematic Universe and its television and streaming offshoots create a wonderful fantasy world of adventure. Fans live vicariously through the characters on screen, and just to be clear, I'm one of them. But we should be careful not to confuse fantasy with reality.
There's a growing minority of violent activist groups in the United States and worldwide. These extremists view their masked terrorism as analogues of Spider Man or Daredevil, concealing their identities and beating the goo out of whoever they deem to be adversaries. The legal reality is that acting this way is likely to land you behind bars. So, at the risk of taking the world of movie magic far more seriously than they were intended to be taken, I'm going to examine a few examples from the MCU against Andrew Branca's 5 elements of self-defense to see whether or not their actions are legally justified.
Captain Marvel vs. Motorcycle Misogynist
The scene in which Captain Marvel steals a bike from an ostensibly sexist biker has become a Rorschach test in the culture war. It's kinda funny if you find the man's actions deeply triggering, and therefore her response deeply gratifying. I've watched the scene several times trying to figure out what made the biker's actions so offensive, but I don't see it. But then, I belong to a generation that actually encourages men to approach women they're interested in. Apparently that's now grounds for assault and grand theft auto.
In the scene, Captain Marvel tells the cat-calling cowboy to hand over the bike or else she will break his hand, which seems a little excessive seeing as how this man is, at worst, kinda bad at talking to women. Woker fans may cheer because (as we know thanks to Gillette) it's viciously, horribly, skyscreamingly bad when a man approaches a woman. But nothing in the law (or generally being a decent human) justifies her actions. The man posed no physical threat, and she was in no apparent danger. Her actions were criminal. She threatened to crush his hand, she stole a motorcycle, she apparently robbed the store, and then she ran someone off the road because...girl power? I guess?
Assault is generally defined as the threat of violence, while battery is the act of violence. In order to engage in that behavior in a legally justified manner, there must be (1) an imminent threat of force which (2) would be perceived as such by a reasonable person, (3) which threat is not provoked by the person claiming self defense, (4) whose response is proportional to the amount of force used, and (5) from which the defender cannot safely retreat. In Captain Marvel's case, the existence of a threat of force would be marginal, at best, even if if she weren't an invincible super "hero". Her response was anythingbut proportional, and she could have easily retreated safely. She fails on 4 of the 5 criteria for legally justified self defense. People find themselves serving time for far less than what Captain Marvel did in this scene.
The Punisher vs. Everyone
I guess I shouldn't say "everyone," since, the Punisher could potentially be justified in using deadly force in some of the scenarios he's depicted in. Sometimes his life was legitimately in danger, and he was attacked without provocation. Sometimes he was operating in a state with Stand Your Ground law, which alleviates the legal duty to retreat from a confrontation. But other times, Frank Castle can accurately be described as a fugitive from justice wanted for multiple homicides. Many of his weapons are illegal for civilians to own, and most of them are illegal in some of the places he's conducting his activities.
In most instances, Frank places himself in danger with the intent to kill people who commit crimes, which while fun to watch, isn't legally permissible. The vigilante investigates and actively participates in violent mayhem. He has killed people who do not present an immediate (if any) threat, and when the threats do exist, he frequently initiated the threat of force. Using the same criteria we used to evaluate Captain Marvel's actions, it's easy to find several examples where Frank Castle failed on all five elements of justified self-defense.
Overall, the Punisher represents one of the worst possible examples of someone relying on self-defense statutes to justify actions. Although portrayed as a sympathetic antihero on the Netflix streaming series, the Punisher is a criminal under the law.
The Hulk vs. Manhattan
The Incredible Hulk does an incredible amount of property damage! Watch the Green Goliath on screen. Entire city blocks are leveled when he jumps into action. Besides the fear of imminent death or grave bodily harm that he routinely causes in villains, friends, and bystanders, it's amazing nobody has sued Bruce Banner or the Avengers. They should give Mr. Incredible their lawyer's number.
But more importantly, people were almost certainly hurt or killed in the crumbling buildings or crumpled up cars due to the Hulk's intentions to "smash." Even if you made the case that Bruce Banner and the Hulk are entirely different people, it's likely that Dr. Banner would still be on the hook for criminally-negligent homicide. I mean, I'm not exactly sure how you would arrest or incarcerate the Hulk. My point is just that the big guy's rampage through New York is not a legally justified use of force.
I know, I know. I'm sucking the fun out of your favorite movies. That's not my intention here. Enjoy the MCU as a fan; I know I will. Just don't look at any movie for good examples of how to employ self-defense in legally, or even really morally justified ways.