"American" or "Association" football ? (Ironically, FA-aka-soccer fields do not have a standard size, only standard boundaries, so they would not be a valid unit of length anyway...)
I used an American football field, and only the length, and my math could be off. When I read “X football fields long” I assume American football, and when I read “X football pitches long” I assume Association football. Or at least I would have, if I had ever encountered it.
“Football field” as a standard is, I believe, based on American football. Which is odd, because American football is non-migratory.
