The WTC had moderately well done escape plans, and I would assume that most who worked there had a general idea of what to do in the event of an emergency. Basketball stadiums have small exits, they are not always well lit in the stands, and there are a lot of people who are at them who are unfamiliar with their surroundings. A bomb goes off, people run to the exits, others go off.. they panic. Look at what has happened at sporting events overseas with stampedes.
This is not overseas. The problems usually come when some moron has chained one of the emergency exits closed, that is the kind of thing to look for. Panic should not be all that contagious.
The people in the WTC didn't know it was a terrorist attack. We've got different circumstances now.