It sounds like you guys were on property that wasn't yours, but that is no reason to be shot at. Especially by an off duty police officer. Him, of all people should know that.
If it was me, I would have stopped where I was at and called 911. Tell them you are being shot at and one of your friends was hit. When the cops show up mr. off duty piggy will have to explain why he was shooting at a bunch of kids riding quads and actually hit one of them. Sounds like it could be attempted murder to me.... None of you were armed or threatening him until after he shot at you.
I'd take the ticket and fine just to see that oinker go down.
Anyways, he was an OFF DUTY cop. He has no right to give tickets or enforce the law any more than you or I. He's a civilian, as were you.
I can understand about messing with peoples hunting spots.
Don't do it. People live for that shit as we live for our sport. Respect that.