Henley sought to present a defense of third person to answer the misdemeanor family violence assault charge. He beat his ex-wife (badly) to prevent her from taking their sons on a weekend custody visit during which he expected, based on history, that the boys would be sexually assaulted by the ex-wife’s boyfriend’s son.
The court held Henley could not assert defense of third person because it was not relevant, characterizing Henley’s “imagined” belief that his boys might be sexually assaulted as speculative and thus, not qualifying as “immediately necessary” to protect them.
Judge Newell dissenting (in Arial, no less) had a strong perspective on this case, and was joined by Judges Keller and Hervey, who also filed their own dissents. Defense lawyers will want to refer to his dissent, which contrasted what you have to show to present a defense (and qualify for an instruction) with the court’s relevance bar to presenting a defense. Judge Hervey wrote along similar lines. Judge Newell also highlighted the court’s misplaced reliance on the need to show imminent harm and suggested that one could reasonably believe immediate action was necessary in the absence of actual imminent harm.
Use the court’s Rule 403 analysis to your advantage. As Judge Newell said, the court’s “Rule 403 analysis  presumes prejudice” instead of presuming admissibility, as the analysis has typically gone. This case gives you another tool to use to fight the state’s evidence: object to relevance and cite this case even when evidence has separate potential for admissibility (think: an extraneous offense or some weird offshoot of facts the state wants a witness to talk about as res gestae).
The court also equated “immediately necessary” with “imminent” (correctly or incorrectly, see Judge Keller’s dissent). After a long search through state law, I couldn’t come up with a good use for this, but one may arise! Keep it in your back pocket.
Finally, for the appellate lawyers: the court says this case is not like Fielder v. State, 756 S.W.2d 309 (Tex. Crim. App. 1988) (battered wife kills sexually dominating husband) because now-CCP 38.36 governs murders and there’s no corresponding statute for misdemeanor assault. If I had the chance, I would give this argument the ol’ “not so fast” treatment: Fielder said 38.36 “in no way broadens or otherwise affects the rules of evidence which apply” and also directly approved of considering the decedent’s past violent conduct as part of the reasonableness of one’s belief supporting (you guessed it) self defense. The court said this “is an established method of proof in self-defense cases, because the law recognizes the fact that future conduct may be reasonably inferred from past conduct.” Fielder, 756 S.W.2d at 319 (quotations omitted). Perhaps in a future case, you can grab some judges from the Henley majority on this point.