Funny, I would have looked in the length area, as that's how it's usually used. Part of the problem is that first you have to decide if it's 100 yards or 120 yards.
I just googled it after your comment and the conversion of football field came in terms of acre or hectare so I think Area is suitable. I will see what most people are using and based on that I will set its value.
I've never heard of anyone comparing to a football field in the Area domain. Of course this is cultural, but at least in the US - the length is what is commonly compared.
Definitely country-specific, I'd expect it to be used to describe areas (and football stadiums be used to describe "number of people"). But footy fields in Australia are typically oval shaped!
"Olympic swimming pools" can be used for length, area or volume (but "Sydney Harbours" are only used for volume).
PS just tried the tool and couldn't find any of the above "units", not even "football fields".
