This term came from Archibold Stadium according to the announcers on the Pittsburgh/Tennessee game. They said the field was unlevel and going one way, the players were running downhill.
Yup - to be specific he (Dan Fouts?) said Archbold had a 2% grade. Because some fields have a midfield that is higher than the sidelines (to aid with drainage), I took this to mean that the grade between the 2 endzones was 2%.
