It will depend on the negligence laws of your state as well as the determination of the insurance claims adjuster dealing with the claim but in general you would normally be found at fault. This is due to you rolling back into the other vehicle and thus many states would consider this negligence in the form of you not being in total control of your car.

There may be some states where negligence laws would place partial blame on the car you hit but only if you could prove they stopped too close to your back bumper and should have had a reasonable expectation that you vehicle may roll back due to the hill.

You can discuss this issue more with your insurance agent to get a better idea of how your insurance company's claim adjusters would find fault in this situation. You may also ask about your state's negligence laws.

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