Physical Danger
Ushers are primarily sedentary creatures, leaving their risk of injury substantially lower than, say, a stunt performer's. Still, there are a few things the unsuspecting usher could accidentally stumble into if he or she isn't careful—ticket paper cuts, anyone? Z'ouch.
Many times, ushers are responsible for menial labor during the "downtime" in between shows or acts. This usually means cleanup, but can definitely include restocking inventory. Have you ever hauled a fifty-pound bag of popcorn kernels down a flight of stairs?
Presuming you lifted with your legs and spared yourself a back injury, there's always the risk of tripping and doing far worse to the rest of you. And just imagine how many times Hannah will whack you with that broom if the bag rips open on the stairs.
Ushers can also be required to help people into darkened auditoriums. These places can be minefields of trash, shallow steps, and people's legs; and that small flashlight you have to keep pointed at the floor can only be so much help. One false step could mean injury for both you and the customer.