The potential for things to really get out of hand is just too large. The security will be massive and the officers and agents are going to be on edge due to the usual terrorist warnings trumpeted in the run-up to any large event lately.
An interesting note about just how massive the security will be; just one part of the RNC security force is - of course - the NYPD. How big a part?
The backbone of security is being provided by the 37,000-member New York Police Department, which has a budget larger than all but 19 of the world's standing armies.