Corrected entry: When April sprays Jessica [Rob] with the pepper spray and he falls down the bleachers, you can see the structures the crew added to fill in the open areas in the bleachers. They were probably added to help keep Rob/stunt double from getting hurt and to keep them from rolling in the proper direction [DVD Version].
Bruce Minnick
25th Nov 2003
Correction: I just re-watched this scene and saw lots of open areas, I did not see any added structures.