Avengers: Endgame - Could Secretly Edited Footage Reveal Hawkeye's Mission?!
2. Hawkeye Is Hunting Stragglers
Those tunnels do look suspiciously like the underground tunnels of Tokyo (New York's are generally older and more dilapidated) and the suggestion that we've only been allowed to see footage from the first act of the movie in the trailers suggests this sequence is from the same Hawkeye scenes as when Black Widow goes to recruit him.
So how would that fit if there are Outriders here? It was assumed that Hawkeye was on a mission hunting Yakuza, but that never really made that much sense. In the context of the probable death of his family, why would he have gone back to a government-type job? Sure, it could be a case of him throwing himself into his work, but isn't it more compelling that he'd be trying to do whatever he could to get some sense of revenge?
Think about it: when Thanos flees at the end of Infinity War when he has snapped his fingers, he leaves alone. He leaves what's left of his Outrider army (which was HUGE) and while half of them were presumably dusted, there must have been survivors. What if they fled too, but without the Space Stone, they were forced to hide on Earth? What if Hawkeye is cleaning up to gain some control of a situation he can't change by doing what he knows - hunting?
This would also explain why he appears to be alone in this sequence. If he's defending against an attack on the Avengers, why would he be doing that alone? Nothing about the footage around the explosion suggests he's operating with anyone else until he's talking to Black Widow and that appears to be the calm after or before the storm.
It would also explain why he's not wearing his new Quantum Realm suit, which we know he will adopt when he's back with the Avengers. So it would seem this comes before that.
Alternatively, of course, this sequence may come later in the movie...
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