In Texas, the law permits two individuals to engage in mutual combat. Under Texas Penal Code section 22.06, a person is engaged in mutual combat if the contact did not cause serious bodily injury or threaten to cause injury, or if the alleged victim took part despite knowing the risk because of their profession.
Therefore, if two people are in a fist fight that did not cause serious bodily injury, and if there was reasonable consent based on words or body language, a mutual combat defense could be used. However, if serious bodily injury occurred or the combat was unprovoked, it likely will not hold up as mutual combat.