The Avengers are back in the Bruce Banner had been in the Hulk state for years on the planet Sakaar. When Banner finally transformed back from the Hulk and discovered that he had lost years of his life, he became even more fearful of changing into his alter ego, fearing that if he did, he might never come back. However, in the epic finale, he willingly transformed into the Hulk in order to fight the film's major antagonist, the devastatingly powerful Hela. After the battle, Banner remained in the form of the Hulk, in the final moments of the film as he stood aboard Thor's starship with the refugees from Asgard.
But in the New York City and in the African nation of Wakanda. The Hulk, meanwhile, only appears in the final shot, running behind Captain America with the rest of a large group of heroes. The Hulk received much more on-screen time in Thor: Ragnarok, but if the trailer is representative of Avengers: Infinity War, then Bruce Banner may once again be the front-and-center half of the pair.
Related: Thor: Ragnarok Wastes Bruce Banner
Banner and the Hulk's moments in the trailer pose a number of immediate questions: how does the Hulk become separated from Thor and return to Earth, especially given that the God of Thunder throughout the trailer appears to be not on Earth? What causes the Hulk to change back into Bruce Banner?
The most logical sequence of events is that Thor's ship is attacked by Thanos per Ragnarok's mid-credits scene, with Loki giving up the Tesseract, many people being killed, and Thor and Banner being flung in separate directions: the former towards the Guardians, the latter Earth. It's also possible that Doctor Strange played a role in bringing the Hulk/Bruce Banner to Earth, although if Strange is involved, then it appears that something went wrong. Falling from the sky, the Hulk arrives with a thud into Dr. Strange's Sanctum Sanctorum... directly through the ceiling (just like the Silver Surfer in the Infinity Gauntlet comic). The impact could be enough to bring Banner out of Hulk form - or Doctor Strange might initiate the transformation - resulting in the first shot of Banner in the trailer; his au naturale entrance clues us in that he has just left being his green alter ego.
The next sequence shows a clothed Banner, with Wong, Doctor Strange and Tony Stark, as destruction comes a-knocking. The Sanctum Sanctorum is located on Bleecker Street in Greenwich Village in the south of Manhattan, which puts it right in the middle of Thanos' attack glimpsed from afar by Peter Parker.
Here's where things get confusing. There are no shots of the Hulk in New York City (nor were there any in the SDCC footage), which doesn't mean that the Green Goliath doesn't appear here, although it does seem likely that Banner won't be too eager to transform anytime soon. Bruce has always been a reluctant hero, and after Ragnarok's troubles, he'll be especially cautious.
Related: Thor: Ragnarok: Did Bruce Banner Commit Suicide?
The next time we see the good doctor is in Wakanda, the African kingdom that the Black Panther rules over and the location of the final Infinity Stone. This would appear to be him reuniting with Black Widow. Banner has been missing for years, ever since their relationship was just beginning to simmer, so this is quite an emotionally loaded moment; the pair's on-screen reunion seems to be subdued and sweet.
What we also have in the shot is the Hulkbuster. An arm is in the background, and in a prior shot we saw it flying to the ground. Obviously, the expected pilot would be Tony Stark, yet he's not seen anywhere in the sequence and so it's been already heavily speculated Banner is in the armor, perhaps as an alternative to him transforming. Of course, this only asks more questions; the final time we see Bruce is when the Hulk is rampaging behind Cap in the final shot, revealing he must eventually become the other guy again.
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Even if this chronological order of events is correct, it's an incomplete journey with a lot not put in the trailer (compared to Captain America, whose role seems considerably clearer). Banner is openly shown in two locations where other characters aren't, made all the more confusing by his expected refusal to Hulk out. Whatever the case, one thing we do know is that Avengers: Infinity War and Avengers 4 are telling one big Hulk arc, so expect some big changes to Bruce in the coming year.
