The 3D Avengers: Endgame trailer reportedly shows that Hawkeye was running from an Outrider during the fiery tunnel scene.
In the latest Avengers: Endgame trailer, Hawkeye can be seen briefly running through a tunnel that suddenly bursts into flames.
The LEGO Avengers: Endgame set for HQ comes with some Outrider minifigures, so this could tie everything together.
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.