Who is in fault if a person pulling out hits someone else who stopped its car all of the sudden?

The car in the back. If you hit a pole, tree or another object with your car, you are At Fault. If a car slams on its breaks in front of you and you rear end them, you are at fault. The reason for this is You are the person responsible for the actions of the vehicle in which you control as the driver. If the conditions around you change, you, who are in charge of the vehicle in direction and speed must change as well.