Toward the end zone or goal line in sports like football, or the direction away from the defending team.
Compound of 'down' and 'field,' originated in American football (late 19th century). 'Down' here comes from the football term for each offensive play, not from a spatial direction.
Here's a confusing bit of sports etymology: 'downfield' doesn't actually mean downhill—it comes from football's 'downs,' the four chances to advance. 'Downfield' means toward the goal line, so sports announcers are accidentally making spatial poetry out of a rule mechanic.
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