The most fundamental of all defenses is the right to defend one’s self from another’s unprovoked attack. In Texas, we simply call that the right to self defense. However, the defendant cannot start the fight. In Smith v. State, the right to self defense was somewhat limited by the Court of Criminal Appeals in 1998. A charge on provocation is required when there is sufficient evidence that the defendant did some act or used some words that provoked the attack on him, and the actor or words were reasonably calculated to provoke the attack, and the act was done or the words used with the intent that the defendant would have a pretext for inflicting harm on the other person.
However, just because someone is charged with aggravated assault with a deadly weapon or assault causes bodily injury/family violence and the alleged victim is the party to an incident who is left with injuries, does not mean that the only defense is self defense. There are a number of defenses to a fight.
On defense in Texas is “mutual combat.” That defense comes into play when both parties consent to the fight.