I found this while playing Stadium and recreated it with my friend. If you spawn on team 2, there are 2 sections of railing on the statue side of the middle point that you can walk through. I found this because I died after walking through the rail on the side and falling off the map.
The clip shows me on Team 1 either being stopped by the railing or if I step on the front pipe piece, I walk onto the railing. My friend on team 2 can walk through 2 sections, one on either side of the point. The rest of the railing on the platforms are solid besides those 2 sections