The 3D Avengers: Endgame trailer reportedly shows that Hawkeye was running from an Outrider during the fiery tunnel scene. The Russo Brothers have admitted to using decoy footage in the upcoming movie to provide misdirects, much like they did with Infinity War. Plus, Kevin Feige has revealed that the majority of the trailer footage released thus far has come from the first 15 to 20 minutes of the movie. However, it looks like they forgot to do some of their clever editing for the 3D trailer.
When the second trailer for Avengers: Endgame more notable scenes of this supposedly happening is when Steve Rogers, Natasha Romanoff, and Rhodey come running outside to look at the sky. There is a large gap between the characters that may be someone else who was edited out to avoid spoilers. Now, there is more evidence that this was the case.
In the latest Avengers: Endgame trailer, Hawkeye can be seen briefly running through a tunnel that suddenly bursts into flames. In the original footage, we see the flames and there is nothing in them. However, a clever Redditor spotted something peculiar in the 3D version. The general consensus is that one of Thanos' Outriders from Infinity War can be seen in said flames. It does appear to be someone, or something, with several appendages, which is where the Outrider theory comes from. It certainly makes sense, but why would Marvel Studio go through the trouble of erasing the fact that Hawkeye is running from an Outrider?
It is possible there were a lot more than just one Outrider on Hawkeye's trail. Maybe the explosion was set on purpose as a way to take down a lot of them. As for where the explosion is taking place, it is believed that it is in the Avengers headquarters after an attack from Thanos or at the very least, his Outriders. The LEGO Avengers: Endgame set for HQ comes with some Outrider minifigures, so this could tie everything together. Plus, the shot of Ant-Man running through a battle scene appears to be in an office environment.
The Russo Brothers have been keeping their mouths shut when it comes to just about anything having to do with Avengers: Endgame and the story. They have broadly talked about making the final movie in the MCU's Phase 3 and finding a way to wrap up eleven years-worth of movies. The task sounds daunting, but the Russos seem pretty calm and collected about the whole situation. With that being said, they will more than likely take a pretty sizable vacation after the promotional tour for Avengers: Endgame winds down in a few months. You can check out the supposed Outrider chasing Hawkeye below, thanks to Reddit.