The person that hit the golf ball and broke your windshield would be the person ultimately responsible for the breaking of your windshield. They are the one whose actions caused your back windshield to be shattered.

If you do not know who the person is that hit the ball into your car's back glass, then you can ask the golf course if their insurance will pay for your damages but typically this would be excluded. The golf course parking lot likely has a sign stating that owner of vehicles are responsible for their cars being parked there and they cannot be held liable.

If you are in the position of not knowing who hit the golf ball into your vehicle and if the golf course will not take responsibility for the damages then you will likely need to put in a claim with your physical damages portion of your insurance policy.

Comprehensive coverage will normally cover glass breakage. You will need to pay the deductible associated with this coverage (unless you are in a state that waives the deductible for glass replacement) but would be able to get your back glass repaired or replaced.