Okay, so I put together a scaled image of what a football field would look like at Bristol Motor Speedway.
Assuming the Allison Terrace and The Allisons sections are the same width as the front straightaway, which measures 650 ft., a football field with endzones would be slightly wider than 1/2 the front straightaway.
Seats will be a good distance from the field... Perhaps they can put some sort of temporary bleachers all the way around the field that wouldn't block the view from the permanent BMS seats.