We would have to look at each situation. Indoor/outdoor, football/basketball, bombs/guns. Lots of variables.
For sure. In an indoor arena, a more efficient panic vector might be "poison gas," even a false poison gas such as gallons of bleach dumped, running down the stairs and under the seats, and evaporating with great stink. A certain percentage will succumb to mass hysteria in such circumstances, and literally pass out. (We see this in high school cafeterias once in a while. It's a well know psychological phenomenon.)
Once that percentage passes out, it will "prove" to many of the others who are smelling the odor that they are indeed witnessing the effects of poison gas. That will in turn trigger the panic stampede.
Panic is the real killer in venues where people are packed together. The trick is for terrorists to engineer the panic in a deliberate manner, to leverage mass casualties from a minor cause.