Tex. Penal Code § 9.63: GUARDIAN-INCOMPETENT.

The use of force, but not deadly force, against a mental incompetent is justified:

(1) if the actor is the incompetent's guardian or someone similarly responsible for the general care and supervision of the incompetent; and

(2) when and to the degree the actor reasonably believes the force is necessary:

(A) to safeguard and promote the incompetent's welfare; or

(B) if the incompetent is in an institution for his care and custody, to maintain discipline in the institution.

Acts 1973, 63rd Leg., p. 883, ch. 399, Sec. 1, eff. Jan. 1, 1974. Amended by Acts 1993, 73rd Leg., ch. 900, Sec. 1.01, eff. Sept. 1, 1994.