Paint damage by Vordermann

Hello together, the following story happened to me: 2-3 weeks ago I was with some buddies on the way to the Baggersee, when a good friend of mine came up with the stupid idea to give a good gas on the gravel parking lot… Of course I was the sufferer and got a whole load of stones etc. on the front and windshield. A few days after this action I noticed a paint damage on the bonnet of my car, which I had not noticed before. Ic h have also several witnesses who can confirm that that “friend” catapulted the cargo of stones on my car to me. He even admitted this until I had addressed him again to the damage… now he does not want to settle the damage. Just for information: this is a 3 month old car, the paint damage did not notice me before. Who is the burden of proof? Who pays? Thanks already in advance!