I have never heard this before hence my low confidence level. However, the corolla of a flower is the contour formed by the petals so I can only imagine that the writer of the text is referring to the outer perimeter and that there is some kind of netting forming the perimeter of the stadium grounds or the stadium itself.

I have seen this comment on the wikipedia article for 'corolle':
Le terme de corolle est souvent employé pour désigner des objets présentant une analogie de forme : robe, parachute, objet décoratif, etc.


I can't see any evidence of the word 'corolla' being any kind of technical term used in English for anything other than a flower so I think that I would play it safe and use the word 'perimeter' in this case.

If you could get any pictures or layouts of the stadium in question or if there are any in the rest of your text, you may be able to check whether this is along the right track.