"Seven people moving at once can bend steel."
It goes way beyond "pushing" when a panicked crowd moves as one.
Most of what scientists know about stampedes comes from anecdotal sources, which suggest that human psychology undergoes a change when people are forced into tight spaces, especially when about 10 people are crowded into one square meter—the equivalent of about 1,000 in a mid-sized classroom. Under such pressure, crowds tend to move as one and ignore alternate exits, accelerating the possibility of disaster.
roger, we're not talking pushing like there is in every high street, every pub bar we're talking crushing like at the Hajj or the Love Parade. The physics is important.