question? the make my day law

if memory serves me right the law goes something more or less along the lines of this "if a person feels threatened after another person comes to their property they can shoot the person who threatened them on their property" or atleast that was my understanding am I missing something or does that mean of a vigilanti came to your property and threatened you, you could shoot them (and if that one bullet just happened to kill them) it would be perfectly legal? or am I misinterpeting the law?