If you want a stadium, there are two Bryce freebies - search for 'stadium' in freestuff.

If it's the pitch you're after, I haven't seen one; but you might be able to paint one and map it onto a flat plane. There are certainly enough soccer nuts on this forum to give you the exact dimensions.

(edit) The two Bryce stadia each have a pitch included. Assuming you have Bryce, you can take your pick.