If you are involved in a rear-end collision, the damages to each vehicle involved will show how the incident occurred. If the only damaged areas of the vehicles include the back of your car and the front of the other, it is clear you were struck from behind. In most situations, you would not be found liable in these situations.
However, if multiple cars are involved, and you are hit from behind and pushed into the car ahead of you, the third-vehicle driver will likely be found at fault.