Despite being the most powerful Avenger, Hulk (Mark Ruffalo) wasn’t able to defeat Iron Man (Robert Downey, Jr.) in Avengers: Age of Ultron. It was one of only a few losses that the Green Goliath has had to endure in the Marvel Cinematic Universe. It also marked the first time that he lost a one-on-one showdown against another MCU character.
Hulk’s fight with Iron Man in the second Avengers movie was as a result of him being mentally influenced by the powers of Scarlet Witch. Hulk went on a mindless rampage until he was opposed by Iron Man, who wore into battle his Hulkbuster armor. Thanks to a massive boost in size and strength, Iron Man was able to pose a physical threat to Hulk in a way that he wouldn’t have in his usual suit of armor. After a long, brutal exchange of blows, Iron Man proved victorious and managed to knock Hulk unconscious.
As a character who’s commonly referred to as “the strongest one there is” in Marvel Comics, Hulk losing to Iron Man was a surprising development. The Hulkbuster armor was designed specifically for beating him, but Hulk has a well-earned reputation for defying the odds and winning all contests of brute strength. However, this was one time Hulk failed to overcome his opponent, and that’s largely due to Iron Man’s sucker punch at the end of the fight.
Hulk was winning when they crashed into a building, causing it to collapse upon them. After emerging from the debris, a winded Hulk sat up, only to be abruptly punched in the face by Iron Man. It was this surprise attack that allowed Iron Man to prevail over him. As for why Hulk was knocked out by this, it’s important to point out that Hulk’s power is fueled by one emotion: anger. Hulk, driven by rage, was in the process of pummeling Iron Man until the building fell and completely disrupted the flow of battle. Hulk was momentarily coming back to his senses when Iron Man hit him. What this means is that at this very moment, Hulk had forgotten his anger. Iron Man won because he was able to take advantage of this sudden turn of events.
In other words, Iron Man would have lost if Hulk’s rage hadn’t subsided. There was a point in the fight when Stark was dominating, but all he did was make Hulk even angrier than he already was. After this, the odds shifted in Hulk’s favor, with the character unleashing a furious onslaught of powerful blows that was doing a number on Iron Man’s Hulkbuster suit. If the fight had continued uninterrupted, Hulk would have handed Iron Man what likely would have been his biggest beatdown.
Unfortunately, this wasn’t the last time that things didn’t go Hulk’s way in a big fight. He had to get help from Grandmaster’s cheating against the God of Thunder in Thor: Ragnarok and was effortlessly defeated by Thanos in the beginning of Avengers: Infinity War. The battle with Thanos, in particular, makes Hulk’s Age of Ultron defeat all the more crushing, as it could have given him a huge win that was denied to him in his later MCU films.