I actually found a discussion page on the internet.
http://ihrrblog.org/2014/07/22/security-risk-sport-mega-events/
From the page: “Sport Mega Events are laboratories for testing innovations in security technology which leads to security models that become standard practice.”
Seems to say because of the big security challenge it has been worked on, its vulnerabilities known and addressed. Crowds are directed to crowd zones.
If the parking lot is also secured from protests, then the large number of people attending the event have plenty of room to get to their cars.
The parking lot is a large area not dedicated to daily life as is the case of a convention center on a city street.
I am working security in both cities and Cleveland has me worried.
Part of the reason I am more confident in Philly is the exceptional performance of the Philly PD during the Pope's visit last year. The coordination with federal partners worked out really well. They blew away all expectations when it came to traffic control and keeping things clear for the motorcades.