re: Is shooting down a drone a civil offense?

If someone pulls into your driveway past a "No Trespassing" sign can you shoot then? Or their car?

For the drone, criminal violation, probably felony, and likely responsibility for paying for the damage you cause, i.e., buying them another drone and whatever it might have been carrying.

Are they breaking the law, probably. Call the police. Unless they try to fly it into your window, in which case, fire away.