This law is to protect the event authorisor's revenue. It would be far cheaper to place your advert on a building overlooking the event, or hire a pilot to air-tow a banner. In that case, no more advertising revenue and no more event.
I suggest that you don't bother trying to challenge this one in court for 3 reasons.
1. the rule was properly passed into law
2. it is clearly and unambiguously written hence grounds to challenge seem "thin" at best; and most importantly
3. You are asking a court to interfere in a revenue stream - they are very much against that (take a look what happens to those who challenge "safety camerea" revenue stream"