A fall on the rib cage can result in injury to the ribs. Injuries can range from minor bruising to multiple rib fractures.
In addition to being painful, a rib injury can often cause problems with breathing, since any deep intake of breath intensifies the pain. It is also painful to walk with a rib injury.
As a first responder there is little you can do to help. If you have a wide elastic bandage (preferably self-adhesive), this can be wrapped around the naked torso to create support for the rib cage. This may reduce pain a little if the accident victim has no choice but to descend.
If the pain is severe, you should make an emergency call and wait for the professional rescue team.