Some time ago I did quite a few stadiums for Nike ads. I used mostly Railclone for geometry and Forrestpack for crowds.
It was quite some time ago so I was a pioneer with using Railclone for stadiums (long before any tutorials on this topic here
and it was a bit of headache then, but guys from Itoo were very helpful as always!
More images and screenshots of the stadium model and some railclone trees
, as always on my website: http://lukx.com/blog/nike-field-generals