Here is my understanding of the Castle Doctrine or Defense of Habitation Law in Texas: a person can reasonably protect him or herself against another person’s use or attempted use of unlawful force. The person acting to protect themselves - you - must not have provoked the other person.  The law covers you from a person who tries to unlawfully or forcefully enters or attempts to enter your place of residence, vehicle, or place of employment. So your front yard would be included.  But you need to be careful as to the circumstances - the facts matter - so I would speak with an attorney if something has happened. Good luck.