Neither. I would use a centimetre.
Usually, you would use kilometers.
yards or meters
Metres, to measure its length or width, square metres to measure its area.
Yards or meters
Meters would be the standard SI (Système international)unit for measuring something the general length of a football field.
A tape measure.
The size of a football field would be measured in square metres (1m*1m) = 1m2.But, if you're trying to measure one-dimension value then you will use metres.Standard "Gridiron" football field is about 5390m2.