If he is outside of your house you may not dispose of him unless he is a mortal threat (coming at you with a knife gun etc).If he is simply larger and/or younger and stronger than you, and attacking you with his fists, would that qualify? What amount of force being used against you would be required to justify shooting the guy there?
If he is struggling with you or tying to get close to you and you have a weapon you are in mortal danger as he may take your weapon and kill you. Off him!