I’ve read that Texas has an “after sundown” kind of law, if someone is on your property in the dark, it’s assumed that they are there to do you deadly harm and you can start firing. Not sure if that’s true or not.
I do not have the law in front of me to cite verbatim, but if the goblin has your property and you have no realistic options to regain possession and they have not left your sight then you can indeed shoot them in the back. I don’t think this is an “after dark” issue either.
Before using this information it would be wise to research it though.