Texas Statutes:
§ 9.31. SELF-DEFENSE. (a) Except as provided in
Subsection (b), a person is justified in using force against
another when and to the degree he reasonably believes the force is
immediately necessary to protect himself against the other's use or
attempted use of unlawful force.
(b) The use of force against another is not justified:
(1) in response to verbal provocation alone;
(2) to resist an arrest or search that the actor knows
is being made by a peace officer, or by a person acting in a peace
officer's presence and at his direction, even though the arrest or
search is unlawful, unless the resistance is justified under
Subsection (c);
(3) if the actor consented to the exact force used or
attempted by the other;
(4) if the actor provoked the other's use or attempted
use of unlawful force, unless:
(A) the actor abandons the encounter, or clearly
communicates to the other his intent to do so reasonably believing
he cannot safely abandon the encounter; and
(B) the other nevertheless continues or attempts
to use unlawful force against the actor; or
(5) if the actor sought an explanation from or
discussion with the other person concerning the actor's differences
with the other person while the actor was:
(A) carrying a weapon in violation of Section
46.02; or
(B) possessing or transporting a weapon in
violation of Section 46.05.
(c) The use of force to resist an arrest or search is
justified:
(1) if, before the actor offers any resistance, the
peace officer (or person acting at his direction) uses or attempts
to use greater force than necessary to make the arrest or search;
and
(2) when and to the degree the actor reasonably
believes the force is immediately necessary to protect himself
against the peace officer's (or other person's) use or attempted use
of greater force than necessary.
(d) The use of deadly force is not justified under this
subchapter except as provided in Sections 9.32, 9.33, and 9.34.
Acts 1973, 63rd Leg., p. 883, ch. 399, § 1, eff. Jan. 1, 1974.
Amended by Acts 1993, 73rd Leg., ch. 900, § 1.01, eff. Sept. 1,
1994; Acts 1995, 74th Leg., ch. 190, § 1, eff. Sept. 1, 1995.
§ 9.32. DEADLY FORCE IN DEFENSE OF PERSON. (a) A person
is justified in using deadly force against another:
(1) if he would be justified in using force against the
other under Section 9.31;
(2) if a reasonable person in the actor's situation
would not have retreated; and
(3) when and to the degree he reasonably believes the
deadly force is immediately necessary:
(A) to protect himself against the other's use or
attempted use of unlawful deadly force; or
(B) to prevent the other's imminent commission of
aggravated kidnapping, murder, sexual assault, aggravated sexual
assault, robbery, or aggravated robbery.
(b) The requirement imposed by Subsection (a)(2) does not
apply to an actor who uses force against a person who is at the time
of the use of force committing an offense of unlawful entry in the
habitation of the actor.
Acts 1973, 63rd Leg., p. 883, ch. 399, § 1, eff. Jan. 1, 1974.
Amended by Acts 1983, 68th Leg., p. 5316, ch. 977, § 5, eff.
Sept. 1, 1983; Acts 1993, 73rd Leg., ch. 900, § 1.01, eff. Sept.
1, 1994; Acts 1995, 74th Leg., ch. 235, § 1, eff. Sept. 1, 1995.
That said:
§ 9.01. DEFINITIONS. In this chapter:
(1) "Custody" has the meaning assigned by Section
38.01.
(2) "Escape" has the meaning assigned by Section
38.01.
(3) "Deadly force" means force that is intended or
known by the actor to cause, or in the manner of its use or intended
use is capable of causing, death or serious bodily injury.
Acts 1973, 63rd Leg., p. 883, ch. 399, § 1, eff. Jan. 1, 1974.
Amended by Acts 1993, 73rd Leg., ch. 900, § 1.01, eff. Sept. 1,
1994; Acts 1997, 75th Leg., ch. 293, § 1, eff. Sept. 1, 1997.
§ 9.02. JUSTIFICATION AS A DEFENSE. It is a defense to
prosecution that the conduct in question is justified under this
chapter.
Acts 1973, 63rd Leg., p. 883, ch. 399, § 1, eff. Jan. 1, 1974.
Amended by Acts 1993, 73rd Leg., ch. 900, § 1.01, eff. Sept. 1,
1994.
In other words, the arrest and prosecution are more than likely in accordance with the law and witness statements on the scene. He may be able to use the Texas statutes as a defense in court though.
I hope to God the fact that he assaulted his girlfriend first is a good chunk of defense