This is so heavily dependent on the facts that it's impossible to give an answer. The general rule is the driver of the car who hits someone from the rear is responsible. The car should not be following so closely and at a rate of speed he or she could not stop.Obviously if the car in front was backing up the general rule goes out the window.There will be multiple claims by the parties. Hopefully each has liability insurance.In most cases the car in the rear will be held responsible for he damage to the car immediately in front, but in multiple car pile-ups sometimes the cars in the rear are tagged for additional damage to the cars further ahead.