Downfield is "in or into the part of the field toward which the
offensive team is headed," according to the Merriam-Webster
dictionary (1), and is consistent with the use of "downfield" in
the football penalty, Ineligible Receiver Downfield. Unfortunately,
as of this date (10-23-11), Merriam-Webster has the same definition
for upfield as it does for downfield (2)!
(1) http://www.merriam-webster.com/dictionary/downfield
(2) http://www.merriam-webster.com/dictionary/upfield