Tex. Penal Code § 9.63
The use of force, but not deadly force, against a mental incompetent is justified:
(2) when and to the degree the actor reasonably believes the force is necessary:
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.