[Joe Bob]

One spouse pulls a car out of the garage, stops just outside and puts down a "box of stuff".......then runs inside the house to get something.....

The other spouse gets in the other car does not look behind the car before starting up. Entry by this spouse to the garage is from the inside the house not outside the garage door, and backs out squashing the "box of stuff".....

Who is at fault?

I will tell you who "I" was later..... to be on topic, it involves an SUV and my SC cabriolet.....