I don't believe that there is a statutory definition of 'protect' in this context. My guess is that the Texas father, who used force to protect his daughter from a sexual assault while it was taking place, would be acquitted, if charged. Of course, the factual analysis, used by prosecutors to determine whether charges should be brought, will focus on reasonableness. If the injuries leading to the attacker's death were incurred in the reasonable scope of protecting the daughter, no charges would be filed. If they conclude that the father continued to fight the attacker after the daughter was secure and the attacker was subdued, then they could determine that the actions were excessive and not protected by self-defense.

Most jurisdictions generally allow the use of deadly force when confronted with deadly force or serious bodily injury, even when the threat of deadly harm or serious injury is to a third person. Sexual assault constitutes serious bodily injury.